Sir Josse d’Acquin: French knight, and Abbess Helewise, at the Hawkenly Abbey in England during the 12th century, by Alys Clare

Christian “Dagger” Daguerre: investigative freelance reporter working for news magnate, Hannibal S. Kydd, by Carl Stevens (Raymond Obstfeld)

Serendipity Dahlquist: gum-snapping 15-year-old girl, and Leo Bloodworth, a grumpy 50-something private investigator, in Los Angeles, California, by Dick Lochte

Jimmie Dale: wealthy dilettante and safecracker by night as the Robin-Hoodish Gray Seal, in New York City, by Frank Packard

Mike Daley: lawyer and ex-priest, in San Francisco, California, by Sheldon Siegel

Adam Dalgliesh: critically acclaimed poet and Scotland Yard commander, in London, England, by P.D. James

Isabel Dalhousie: Scottish-American editor of the esteemed Review of Applied Ethics and a woman of independent means in Edinburgh, Scotland, in the Sunday Philosophy Club mysteries by Alexander McCall Smith

Eve Dallas: homicide lieutenant in futuristic New York City, by J.D. Robb

Nick Dallas: young but retired cop, now a private investigator, in 1950s Detroit, Michigan, by P.S. Elsner

Daisy Dalrymple: a journalist in Hampshire, England, by Carola Dunn

Quintilian Dalrymple: private investigator in 2020s Edinburgh, Scotland, by Paul Johnston

Joe Dalton: sheriff in Metropolis, Illinois, by Lonnie Cruse

Mackenzie “Mack” Dalton: owner of a bar in Milwaukee, Wisconsin, with Synesthesia, a neurological condition enabling her to smell noises or taste color, in the Mack’s Bar Mysteries by Allyson K. Abbott (Beth Amos)

Micah Dalton: “cleaner” for the CIA, roaming the world to fix up Company messes, by David Stone (Carsten Stroud)

Smokey Dalton: African-American unlicensed private investigator, in Memphis, Tennessee, by Kris Nelscott

Justine Dalvik: in Hässelby, Sweden, by Inger Frimansson

Celcius Daly: Catholic detective inspector, in Belfast, Northern Ireland, by Anthony J. Quinn

Superintendent Andrew Dalziel and Sergeant Peter Pascoe, a pair of police inspectors in Yorkshire, England, by Reginald Hill

Gloria Damasco: Hispanic detective in the San Francisco Bay Area, in California, in the Brown Angel mysteries, by Lucha Corpi

Bill Damen: filmmaker turned sleuth, in the San Francisco Bay Area, California, by James Calder

Chief Inspector Damiot of the Paris police, and his dog Fric-Frac, in Paris and elsewhere in France, by Vincent McConnor

Phil Damon: bandleader playing jazz in 1963 San Francisco, California, by John Morgan Wilson & Peter Duchin

Kathryn Dance: investigator with the California Bureau of Investigation, by Jeffery Deaver

April Dancer: the Girl from U.N.C.L.E. (TV tie-in), by Michael Avalone

Eddie Dancer: ex-cop private investigator in Calgary, Alberta, Canada, by Mike Harrison

Jim Dandy: retired physical therapist, and Dodee Swisher, a gallery owner, in North America, in the Elderhostel Mysteries by Peter Abresch

Timothy Dane: private investigator in New York City, by William Ard

Abigail Patience Danforth: 19th century heiress detective, by Marian J. A. Jackson

Bob Danforth: CIA special ops officer dealing with terrorists starting at the 2004 Olympic Games in Greece, by Joe Badal

Judah Daniel: freedwoman who is also the local herbalist, and Narcissa Power, a young widow, at the time of the Civil War in Virginia, by Ann McMillan

Louisa Daniel: 60-ish social worker, and later her daughter Emily and son-in-law David, by Malinda M. Hall

Vic Daniel: 6-foot-7+ cut-rate private investigator, driving a Nash Metropolitan, in Los Angeles, California, by David M Pierce

Boone Daniels: private investigator who would rather be surfing, in San Diego, California, by Don Winslow

Charmian Daniels: police detective in Deerham Hills, England, by Jennie Melville (Gwendoline Butler)

Lt. Jacqueline “Jack” Daniels: in the Violent Crimes unit in Chicago, Illinois, by J.A. Konrath

Dimitri Danilov: Colonel in the Moscow People’s Militia, later the Organized Crime Bureau, and William Cowley, an FBI agent and Russian expert, by Brian Freemantle

Peaches Dann: absent-minded 50-something widow in North Carolina, by Elizabeth Daniels Squire

Dick Dansoir: gay personal trainer and occasional go-go dancer at the boys' bars in New Orleans, Louisiana, by Greg Herren

Joe Dante: maverick cop in New York City, by Christopher Newman

Michel Danton: police detective in the south of France, by Norman Bogner

Lord Charles Danvers, fictionalized Victorian true crime in mid-19th century England, by Donna Fletcher Crow

Daquin: gay police detective, in Paris, France, by Dominique Manotti

Lady Darby: an anatomist’s widow taking refuge at her sister’s estate, in 1830s Scotland, by Anna Lee Huber

Lord Darcy: Chief Investigator for the Duke of Normandy, in contemporary times of an alternative history Anglo-French empire where the laws of magic prevail, by Randall Garrett

Antonia Darcy: librarian at the Military and Naval Club, and grandmother, along with Major Hugh Payne, in London, England, by R.T. Raichev

Fitzwilliam Darcy and Elizabeth Bennet, taking up the story ended in Jane Austen’s Pride and Prejudice, in Regency (early 1800s) England, by Carrie Bebris

Meg Darcy: working-class lesbian private investigator, and police detective Sarah Lindstrom, in St. Louis, Missouri, by Jean Marcy

Tess Darcy: bed-and-breakfast owner in Victoria Springs, Missouri, in the Iris House mysteries, by Jean Hager

Angel Dare: retired porn star running Daring Angels, an adult modeling agency, in Van Nuys, California, by Christa Faust

Candyce “Dyce” Dare: single mom and proprietor of Daring Finds, a furniture refinishing store in fictional Goldport, Colorado, by Elise Hyatt (Sarah D’Almeida)

Madeline Dare: former dubutante in 1980s New York and Massachusetts, by Cornelia Read

Paul Dark: a seasoned MI-6 agent with a past, in a trilogy set in late 1960s Europe and Africa, by Jeremy Duns

Max Darling: investigator, and Annie Laurance, a mystery book store owner, in Broward’s Rock, South Carolina, in the Death on Demand series, by Carolyn G. Hart

Professor John Darnell: detective debunking supernatural theories early in the 20th century, by Sam McCarver

Sigismondo da Roca: Italian agent of a Renaissance duke by Elizabeth Eyre (Susannah Stacey)

D’Artagnan, Athos, Porthos, and Aramis, of Dumas fame, serving the king in 17th century France, in the Musketeers mysteries, by Sarah D’Almeida

Jan Da Silva: lounge singer and private detective, in Seattle, Washington, by K.K. Beck

Captain Jose da Silva: supercop in Rio de Janeiro, Brazil, by Robert L. Fish

Dave: ex-cop investigator, and Mom, Dave’s mother, in Mesa Grande, Colorado, by James Yaffee

Alphonse "Dave" Davecki: police detective in Superior, Wisconsin, by Mike Savage

“Dangerous” Davies: detective constable in north London, England, by Leslie Thomas

Lucas Davenport: police detective and war games designer in Minneapolis, Minnesota, by John Sandford

Charlotte “Charley” Davidson: part-time private investigator helping the police with her ability to contact the dead in her full-time role as the Grim Reaper, in Albuquerque, New Mexico, in a paranormal romantic suspense series by Darynda Jones

Kate Davidson: yoga instructor in Seattle, Washington, and her German shepherd sidekick Bella, in the Downward Dog mysteries by Tracy Weber

John Davies: by Margot Bennett 

Dr. R.V. Davie: of St. Nicholas College, Cambridge, England, by V.C. Clinton-Baddeley

Rebecca Davies: child of privilege running a home for desperate women, and Marshall Webb, Rebecca’s beau, a freelance reporter for Harper’s Weekly who secretly pens dime novels, by Troy Soos

Queenie Davilov: struggling screenwriter and investigator in Hollywood, California, by Denise Osborne

Georgia Davis: ex-cop private investigator, in Chicago, Illinois, by Libby Fischer Hellmann

Angie DaVito: TV soap opera producer in New York City, by Louise Shaffer

Patrick Dawlish: who works with British Intelligence and later at Scotland Yard, by Gordon Ashe (John Creasey)

Darko Dawson: CID detective in Accra, Ghana, by Kwei Quartey

Carla Day: 20-something, and her elderly father, an accomplished Egyptologist suffering from Alzeimer’s, in California, by Diana O’Hehir

Jane Day: newspaper reporter, and Jerry Knight, a talk show host, in Washington DC, by Ron Nessen and Johanna Neuman

Julian Day: seeking revenge against those who ruined his career:, by Dennis Wheatley

Dr. Clyde Deacon: President McKinley’s former physician, who moves to Fairfield, New York in 1902, by Scott Mackay

Polly Deacon: escaping Toronto for a cabin in the back woods, somewhere in Canada and elsewhere, by H. Mel Malton

William Deacon: magazine writer, by Herbert Brean

Mechelle Deakes: African-American police detective demoted to the cold case unit, in Atlanta, Georgia, by Lynn Abercrombie (Walter Sorrells)

John Deal: building contractor in Miami, Florida, by Les Standiford

Hailey Dean: former assistant district attorney in Atlanta, now a therapist and TV personality in New York City, by Nancy Grace

Jeffrey Dean: ex-CIA courier and journalist, now a rare book dealer, in Los Angeles, California, by Wayne Warga

Sam Dean: Jamaica-born black journalist in London, England, by Mike Phillips

Sarah Deane: graduate student, and Alex McKenzie, a doctor in Maine, by J.S. Borthwick

Sarah Dearly: a fledgling vampire working with master vampire Thierry de Bennicoeur, an agent of the Ring, policing vampires worldwide, in the Immortality Bites mysteries by Michelle Rowen

Eve DeCateur, ex-beauty queen, and Annie Capshaw, recently divorced, in Arlington, Virginia, in the Cooking Class mysteries by Miranda Bliss

Dewey Decimal, protecting library resources in a ruined, dystopian New York City, by Nathan Larson

Commander Bill Decker, Mitch Taylor, Jub Freeman, police detectives in New York City, by Lawrence Treat

Manny Decker: detective sergeant with martial arts skills, in New York City, by Marc Olden

Peter Decker: LAPD detective, and his wife Rina Lazarus, in Los Angeles, California, by Faye Kellerman

Sergeant Decker: frontier lawman in 1860s British Columbia, Canada, by Stanley Evans

Robert De Clerq: member of the Special X department of the Royal Canadian Mounted Police in Vancouver, British Columbia, Canada, by Michael Slade

Mr. Dee: in England by Desmond Cory

Judge Dee: magistrate in China during the Tang Dynasty (600s), by Robert Van Gulik

Catherine “Cat” Deean: part-owner of a catering enterprise in Los Angeles, California, in the the Mysteries for Food Lovers, by Cynthia Lawrence

Artie Deemer: jazz aficionado supported by his dog Jellyroll, a movie and dog-food commercial star, in New York City, by Dallas Murphy

Carolus Deene: ex-commando turned schoolmaster in England, by Leo Bruce

Howard Moon Deer: private investigator in San Geronimo, New Mexico, by Robert Westbrook

Rinus de Gier, Henk Grijpstra, and the Commisaris, police detectives in Amsterdam, The Netherlands by Janwillem Van de Wetering

Dr. Gerritt DeGraaf: forensic pathologist in Chicago, Illinois, by Barbara D’Amato

Jade de Jong: private investigator returning home 10 years after her police commissioner father was killed, and police superintendent David Patel, in Johannesburg, South Africa, by Jassy Mackenzie

Sam Deker: 35-year-old Israeli counterterrorism agent and demolitions expert, by Thomas Greanias

Jurrian DeKok: (De Cock in original publications), detective inspector in the police department, in Amsterdam, The Netherlands, by A.C. Baantjer

Kate Delafield: lesbian homicide detective in Los Angeles, California, by Katherine V. Forrest

Marguerite de Landois: in 1899-1900 Paris, France, by Lisa Appignanesi

Edward X. “Iron Balls” Delaney: retired chief of detectives in New YorkCity, by Lawrence Sanders

Evan Delaney: adventurous young woman in Santa Barbara, California, by Meg Gardiner

Frank Delaney: world-traveling investigative journalist and sometime spy, based in Montreal, Québec, Canada, by Michael E. Rose

McLeod Delaney: Pulitzer-Prize-winning journalist from Florida, who comes to Princeton University as a visiting lecturer, later professor, in Princeton, New Jersey, by Ann Waldron

Patricia Delaney: private investigator in Cincinnati, Ohio, by Sharon Gwyn Short

Sarah Booth Delaney: unconventional Southern Belle in Zinnia, Mississippi, in the Southern Belle mysteries by Carolyn Haines

Alex Delaware: child psychologist in Los Angeles, California, by Jonathan Kellerman

Jade del Cameron: ambulance driver in WWI and adventurer in 1919-1920s colonial East Africa, by Suzanne Arruda

Kit DeLeeuw: Wall Street shark turned suburban detective in Rochambeau, New Jersey, by Jon Katz

Ralph Delchard: soldier and Gervase Bret, a lawyer, in 11th century England, in the Domesday Series, by Edward Marston

Petra Delicado: ex-lawyer police inspector, and her sidekick, sergeant Fermín Garzón in Barcelona, Spain, by Alicia Giménez-Bartlett

Alex Delillo: police detective lieutenant in Pasadena, California, by Scott Frost

Jack Delmas: private investigator from the Mississippi Gulf Coast, by Martin Hegwood

Carmine Delmonico: police lieutenant in a fictional mid-1960s college town, Holloman, Connecticut, by Colleen McCullough

Barry Delta: parole officer in Vancouver, British Columbia, Canada, by Dennis E. Bolen

Cat DeLuca: private investigator operating the Pants On Fire Detective Agency specializing in cheating spouses, in Chicago, Illinois, by K.J. Larsen

Commissario De Luca: former commander in Mussolini’s political police, in northern Italy in 1945, by Carlo Lucarelli

Flavia de Luce: an 11-year old sleuth and aspiring chemist in 1950, in the small village of Bishop’s Lacey, England, by Alan Bradley

Nick Delvecchio: private investigator in Brooklyn, New York, by Robert J. Randisi

Bascot de Marins: Templar Knight recovering from imprisonment in the holy lands, in the early 1200s, in England, by Maureen Ash

Gregor Demarkian: former FBI department head in Philadelphia, Pennsylvania, by Jane Haddam

Joe DeMarco: lawyer and trouble-shooter for the Speaker of the House, as Counsel Pro Tem for Liaison Affairs, based in Washington, DC, by Mike Lawson

Leo Demidov: secret police officer in 1950s Moscow, Russia, by Tom Rob Smith

Mary Teresa Dempsey: 5'2" 200 lb. nun in Chicago, Illinois, by Monica Quill (Ralph M. McInerny)

Skye Denison: school psychologist in Scumble River, Illinois, by Denise Swanson

Sergeant Denny and Major Mearns special agents for William Pitt to watch George III, in England, by Gwendoline Butler

John Denson ex-reporter and ex-army intelligence operative, in Seattle, Washington, by Richard Hoyt

General Denton: expatriate U.S. Civil War veteran and former frontier sheriff turned novelist, in turn of the 20th century London, England, by Kenneth Cameron (Gordon Kent)

Hanna Denton, returning home to take over her grandmother’s pie shop, in fictional Crystal Cove, California, in the Pie Shop mysteries by Carol Culver

Harry James Denton: ex-newspaper reporter turned private investigator in Nashville, Tennessee, by Steve Womack

Department Z: and tales of British counterespionage, by John Creasey

Justin de Quincy: bastard son of a bishop in 12th century England, by Sharon Kay Penman

Duke de Richleau, an exiled French monarchist, along with “Modern Musketeers” Richard Eaton, a conservative Christian Englishman, Simon Aron, a liberal Jew, and American Rex Van Ryn, from 1894-1960, by Dennis Wheatley

Leo Desroches: Aboriginal Issues reporter with gambling and drinking problems, born to a Cree mother, in Edmonton, Alberta, Canada, by Wayne Arthurson

Robyn Devara: field biologist, ecologist, and amateur sleuth, based in western Canada, by Karen Dudley

Devereaux: AKA The November Man, a field intelligence agent for R Section, in New York City, by Bill Granger

Sean Devereaux, a detective sergeant, and his friend John Hale, an ex-cop, private investigator, in Auckland, New Zealand, by Ben Sanders

Fever Devilin: folklorist and native of the Georgia Appalachians, by Phillip DePoy

Jude Devine: lesbian ex-FBI agent, now a Montezuma County Sheriff’s detective in Utah, by Rose Beecham

Benedict Devlin: Garda detective inspector, in the borderlands of Ireland, by Brian McGilloway

Harry Devlin: solicitor in Liverpool, England, by Martin Edwards

Jack Devlin: ex-Secret Service agent turned security firm investigator, in the USA, by John Clarkson

Liam Devlin: 1940s IRA hero in Ireland, by Jack Higgins

Matt Devlin: private eye, and Brooke Cassidy, a mystery writer, in 1890s Newport, Rhode Island, by Mary Kruger

Paul Devlin: police detective in New York City, by William Heffernan

Betsy Devonshire: needlework shop owner in Excelsior, Minnesota, by Monica Ferris

Timothy Dewer: police inspector in England, by Hilary Landon (George Bellairs)

Claire DeWitt: the world’s foremost private investigator, in post-Katrina New Orleans, Louisiana, by Sara Gran

Holly Dewitt: film producer and single mother in Miami, Florida, by Sherryl Woods

Manny DeWitt: lawyer for an international firm, Lobbe Industriel, who becomes a spy, by Peter Rabe

Sir John de Wolfe: the crowner (coroner), in 12th century Devon, England, in the Crowner John series by Bernard Knight

Angelique De Xavier: police officer in Glasgow, Scotland, by Christopher Brookmyre

Dexter: blood spatter technician for Miami Dade Police Department, and sociopathic serial killer in Florida, by Jeff Lindsay

Alison Dexter: a detective sergeant, and John Underwood, detective inspector, in New Bolden, Cambridgeshire, England, by Ed O’Connor

Hermes Diaktoros, the Fat Man, a mysterious investigator from Athens, Greece, by Anne Zouroudi

Emma Diamond: recent widow, novice bridge player, and amateur detective, in Houston, Texas, in the Bridge Club mysteries by Honor Hartman (Dean James)

Eve Diamond: reporter for the Los Angeles Times, in Los Angeles, California, by Denise Hamilton

Jake Diamond: private investigator who is more over-easy than hard-boiled, in San Francisco, California, by J.L. Abramo

Peter Diamond: homicide detective in Bath, England, by Peter Lovesey

Venus Diamond: U.S. Fish & Wildlife agent in Washington, by Skye Kathleen Moody

Don Diavolo by Stuart Towne (Clayton Rawson)

Charles Dickens and Wilkie Collins, 19th century writers in London, England, by  William J. Palmer

Delilah Dickenson: owner of a travel agency in Atlanta, Georgia, in the Literary Tour mysteries by Livia J. Washburn

Auguste Didier: master chef in Victorian London, England, by Amy Myers

Alessandro Di Ganzarello, Jennifer Norrington, and Coleridge Tucker, a James Bond-like trio in London, England, by Ivor Drummond (Roger Erskine Longrigg)

Slippery Jim (James Bolivar) diGriz, the galaxy’s greatest interstellar thief and con artist, in the 30th century, by Harry Harrison

Joe Dillard: jaded lawyer in rural Tennessee, by Scott Pratt

George Porter Dillman: yacht-builder-turned-actor-turned-detective, by Conrad Allen (Edward Marston)

Bob Dillon, a pest exterminator in Queens, New York, and Klaus Müller, an assassin, in the Assassin Bug thrillers by Bill Fitzhugh

Sean Dillon: RA enforcer turned British special agent, in Ireland, by Jack Higgins

Jeff DiMarco: insurance investigator in Boston, Massachusetts, by Doris Miles Disney

Aunt Dimity: a romantic ghost in England, by Nancy Atherton

Frank DiPalma martial arts thrillers, by Marc Olden

Laura Di Palma: corporate lawyer in San Francisco, California, by Lia Matera

Gil Disbro: young, conservative, non-drinking private investigator, in Cleveland, Ohio, by James E. Martin

Jocelyn “Joe” Dixon: detective sergeant in New York City, by Richard Wormser

Maisie Dobbs: psychologist and investigator based in 1920s and 1930s London, England, by Jacqueline Winspear

John Dobie: Professor of Mathematics in Cardiff, Wales, by Desmond Cory

Bobby Dodge: a state police sniper, and D.D. Warren, a police detective, in Boston, Massachusetts, by Lisa Gardner

Harold Dodge: 50-ish, overweight former car salesman, in Los Angeles, California, by Philip Reed

Lark Dodge: bookseller in Shoalwater, Washington, by Sheila Simonson

Rev. Charles Dodgson (Lewis Carroll) and Dr. Arthur Conan Doyle team up in 1880s Victorian England, by Roberta Rogow

Trixie Dolan and Evangeline Sinclair, aging actresses in London, England, by Marian Babson

Duffy Dombrowski: Elvis-loving boxer and social worker, and his basset hound, Al, in a town near New York City, by Tom Schreck

Ulysses Finnegan Donaghue: Shakespeare scholar and private eye in Provence, France, by Anna Shone

Neal Donahoe: Harbor Patrol officer, and Tory Lennox, a Coast Guard lieutenant, in Santa Barbara, California, by Tony Gibbs

Krissie Donald: a parole officer in Scotland, by Helen FitzGerald

Raymond Donne: former NYPD detective, now a teacher in his old precinct, in Williamsburg, Brooklyn, New York, by Tim O’Mara

Donovan: assistant to Danny Coyle, a gambler, by Judson Philips

Donovan family, involved in a global gem-trading empire, based in Seattle, Washington, by Elizabeth Lowell (A.E. Maxwell)

Bill Donovan: Chief of Special Investigation, in New York City, by Michael Jahn

Cal Donovan, Frank Shapiro, and Liz Graham, cops in Castlemere, England, by Jo Bannister

Jake Donovan: FBI profiler by John E. Douglas

Joe Donovan: former investigative journalist whose son has disappeared, in Newcastle, England, by Martyn Waites

Maura Donovan, fulfilling her grandmother’s wish by returning from Boston to the original family home in the small town of Leap, Ireland, in the County Cork mysteries by Sheila Connolly

Molly Donovan: reporter in Devil’s Harbor, Oregon, by Carolyn J. Rose & Mike Nettleton

Paul Donavan: by Carter Brown

Delilah Doolittle: British widow and pet detective, and Watson, her Doberman pinscher, in fictional Surf City (Huntington Beach), California, by Patricia Guiver

Jackson Donne: ex-cop private investigator, or night security guard when times are hard, in New Brunswick, New Jersey, by Dave White

Shawn Donnelly: police detective, in Detroit, Michigan, by Therese Szymanski

Eliza Doolittle and Henry Higgins, the flower girl and professor, as amateur sleuths beginning in 1913 London, England, by D.E. Ireland

Lorna Doria and Donna Miro in Massachusetts and New York City, by Heather Graham

Carroll Dorsey: private investigator in Pittsburgh, Pennsylvania, by Thomas Lipinski

John Dortmunder: criminal master planner in New York City, by Donald E. Westlake

William Dougal: post-grad student and security firm employee, in England, by Andrew Taylor

Frances Doughty, the young daughter of a pharmacist, and an amateur sleuth (later professional detective), in Victorian London, England, by Linda Stratmann

Rick Dover: a homicide detective in Los Angeles, California, by Mark Bouton

Wilfred Dover: fat lout of a Chief Inspector in England, by Joyce Porter

Emmeline (Em) Dowell: glassblower in Tucson, Arizona, in the Glassblowing mysteries by Sarah Atwell

Father Roger Dowling: St. Hilary’s parish priest in Fox River, Illinois, by Ralph M. McInerny

Arthur Conan Doyle: doctor, author, and student of the paranormal, in late 19th century London, England, by Mark Frost

Arthur Doyle: young doctor, and Joseph Bell, a doctor and Doyle’s mentor, in Edinburgh, Scotland, by David Pirie

Arthur Conan Doyle and Charles Dodgson (Lewis Carroll) team up in 1880s Victorian England, by Roberta Rogow

Gemma Doyle: transplanted Englishwoman returning to run her Great Uncle Arthur’s Sherlock Holmes Bookshop and Emporium, along with Moriarty the cat, in West London on Cape Cod, Massachusetts, by Vicki Delany

Huck Doyle: pro golfer and non-practicing lawyer working as a private investigator, in Los Angeles, California, by Don Dahler

Jack Doyle: failed ad-man and reluctant sleuth working in the horse-racing world, based in the Chicago, Illinois area, by John McEvoy

Kit Doyle: radio talk show host and amateur sleuth, in California, by Bonnie Hearn Hill

Molly Doyle: antiques dealer in Carmel, California, by Elaine Flinn

Earl Drake: bank robber, killer, and part-time tree surgeon, later a secret agent, by Dan J. Marlowe

Jessie Drake: homicide detective in Los Angeles, California, by Rochelle Krich

Simon Drake: Chicago lawyer transplanted to southern California, by Helen Nielsen

Stephen Drake: newspaper reporter with ESP in San Francisco, California, by Collin Wilcox

Steve Drake: former actor turned private investigator, based in New York City, by Richard Ellington

Stud Draqual: maybe gay, maybe not CEO of Draqual Fashions, and a much-in-demand New York City haute-couture fashion designer of ladies' silk underwear, by William Maltese

Harry Dresden: the only wizard listed in the yellow pages in Chicago, Illinois, in the Dresden Files by Jim Butcher

Sir Clinton Driffield: Chief Constable, and Squire Wendover, in rural England, by J.J. Connington

Ben Driskill: lawyer dealing with major political conspiracies, in New York, Iowa, and elsewhere, by Thomas Gifford

Clifford Driscoll: no-named American spy in New York City, by William L. DeAndrea

John W. Driscoll: homicide detective lieutenant in New York City, by Thomas O’Callaghan

Honey Driver: owner of the Green River Hotel and amateur sleuth, in Bath, England, by J.G. Goodhind

Jimmy Drover: ex-sportswriter in Chicago, Illinois, by Bill Granger

Chester Drum: ex-FBI agent private investigator, venturing around the world, by Stephen Marlowe

Nicholas Drummond: American-born chief inspector at Scotland Yard, London, England, in the Brit in the FBI series by Catherine Coulter & J.T. Ellison

Major Sean “Bulldog” Drummond: lawyer in the army's Judge Advocate General Corps (JAG), by Brian Haig

Sam Dryden: former Special Forces operative retired to a small town on the coast of southern California, in a series of high-tech thrillers by Patrick Lee

Alex Duarte: ATF agent and Bosnia veteran, by James O. Born

Tubby Dubonnet: lawyer in New Orleans, Louisiana, by Tony Dunbar

Kenneth Ducane (also called Vandoran), chief of the Secret Intelligence Service, in England, by John Bingham

Nell Duckworth: a botanist, and Geoffrey Binswanger, a biologist, investigate a South Pacific island (and other places) where evolution went off in a different direction, by Warren Fahy

Imogene Duckworthy: 22-year-old waitress, living with her mother Hortense, and baby daughter Nancy Drew, in Saltlick, Texas, by Kaye George

Ray Dudgeon: former newspaper reporter turned private investigator, in Chicago, Illinois, by Sean Chercover

MacDougal Duff: retired history professor in New York City, by Charlotte Armstrong

Nick Duffy: bisexual ex-cop turned private investigator, in London, England, by Dan Kavanagh

Sean Duffy: detective sergeant in 1980s Northern Ireland, in the Troubles Trilogy by Adrian McKinty

Dugan: a lawyer, and his wife Kirsten, owner of the Wild Onion, Ltd, a private detective agency, in Chicago, Illinois, by David J. Walker

Charles Matthieu Beuvron du Luc: teacher of rhetoric at Louis le Grand, a Jesuit school in 1680s Paris, France, by Judith Rock

Peter Duluth: alcoholic theatrical producer, and Iris Pattison, an actress (and later wife), in California, Mexico City, and New York City, by Patrick Quentin

Daphne du Maurier: young aspiring author in 1920s Cornwall, England, by Joanna Challis

Max Dumas: by Carter Brown

Cliff Dunbar: former English professor turned private investigator, in Los Angeles, California, by Will Harriss

Eve Duncan: forensic sculptor by Iris Johansen

Vanessa Duncan: schoolteacher in late 19th century Cambridge, England, by Catherine Shaw

Tom Dunjer: in the future, by Isidore Haiblum

Luke Dunlop: an agent for the Witness Protection Agency in Australia, by Peter Corris

Mara Dunn: French-Canadian interior decorator, relocated to the Dordogne region in southwestern France, by Michelle Wan

Micah Dunn: a private investigator in New Orleans, Louisiana by M.K. (Malcolm) Shuman

Okie Dunn: appointed sheriff in 1930s Vernon, Oklahoma, by Fred Harris

Fintan Dunne: hard-boiled detective in pre-World War II New York City, by Peter Quinn

Nicodemus Dunne: a fallen Bow Street Runner working as a running patterer, spreading the daily news by word of mouth, transported to 1828 Sydney, Australia, in the Curious Murder mysteries by Robin Adair

C. Auguste Dupin: detective in the first “real” detective story, by Edgar Allan Poe

Georges Dupin: former Paris detective, now a police Commissaire exiled to Brittany, France, by Jean-Luc Bannalec

Gabriel Du Pré: Métis (Cree and French, maybe a little English) cattle inspector and sometimes sheriff in Montana, by Peter Bowen

Cat Dupree: bounty hunter after her father’s murderer in Mexico, by Sharon Sala

M. Dupuy by Anthony Gilbert

Quincy Durant and Artie Wu, a couple of soldiers of fortune for their company, WuDu Ltd., by Ross Thomas

Sam Durell: Cajun CIA operative, by Edwards S. Aarons and later Will. B. Aarons

Gus Dury: failed journalist turned investigator, in Edinburgh, Scotland, by Tony Black

Starletta Duvall: black homicide lieutenant in Brookport, Massachusetts, by Judith Smith-Levin

Jack Dwyer: ex-cop, part-time actor, and security guard, in Cedar Rapids, Iowa, by Ed Gorman

Billy Dye: struggling author, and Rawhead, an assassin and Dye’s childhood friend, in Manchester, England, by David Bowker

Mandy Dyer: owner of Dyer's Cleaners in Denver, Colorado, by Dolores Johnson

Toby Dyke: reporter in Devon, England, by E.X. Ferrars

Lindsey Dyson: investigative reporter by Calley Moore