Mabry, Bubba: a private investigator in Albuquerque, New Mexico by Steve Brewer

Mabry, Caroline: a police detective in Spokane, Washington by Jess Walter

MacAlister, Marti: a widowed black police detective in Lincoln Prairie, Illinois by Eleanor Taylor Bland

MacAllister, Frank: a swashbuckling private investigator in Brazil by Ritchie Perry

MacBean, Elsie “Beanie”: a freelance writer and a member of the Was hoe Tribe and her basset hound, Cruiser, in South Tahoe, Nevada by Sue Owens Wright

Macbeth, Hamish: police constable in Scotland by M.C. Beaton

MacBride, Grace: founder of Monkeewrench, a game software company in Minneapolis, Minnesota by P.J. Tracy

MacDonald, Devon: a private investigator in St. Paul, Minnesota by Nancy Baker Jacobs

MacDonald, Paul: ex-reporter and mystery writer in San Francisco. California by Julie Smith

MacDonald, Robert: an inspector/superintendent  by E.C.R. Lorac 

MacDonell, Dr. Duncan A.:   a veterinarian in Houston, Texas by Robert E. Armstrong

MacGowan, Maggie: a documentary filmmaker in Los Angeles, California by Wendy Hornsby

Mackay, Kathryn: prosecuting attorney in northern California by Christine McGuire

MacKinnon, Scotia:   former police officer turned private eye in Friday Harbor, San Juan Island, Washington by Sharon Duncan

Macklin, Peter: hit man for the mob in Detroit, Michigan by Loren D. Estleman

Mackey, Herbert: a sheriff in Blanco County, Texas by Ben Rehder

MacLeish, Cooper: a taxi driver and Vietnam vet in Chicago, Illinois by Sam Reaves

MacLeod, Chanse: a gay private investigator in New Orleans, Louisiana by Greg Herren

MacPherson, Annie: an attorney in Seattle, Washington by Janet Smith

MacPherson, Elizabeth: forensic anthropologist in the Southern US by Sharyn McCrumb

Madden, David: a postal inspector by Doris Miles Disney

Madden, John: Scotland Yard Inspector and shell-shocked veteran of World War I by Rennie Airth

Maddox, Ivor: sergeant at the Wilcox Avenue Station in Hollywood, California by Elizabeth Linington

Madriani, Paul: defense attorney in California by Steve Martini

Madrid, Nick: a freelance journalist by Peter Guttridge

Magaracz, Nick: Private Eye in Trenton, New Jersey by Kate Gallison

Maglione, Gianna: lesbian police lieutenant in Washington D.C. by Penny Mickelbury

Maguire, Cormac: an Irish archaeologist in Ireland by Erin Hart

Maguire, Maggie: an ex-Pinkerton agent in 1870s San Francisco, California by Kate Bryan

Maigret, Inspector Jules: Maigret, Inspector Jules: a police inspector in Paris, France by Georges Simenon

Maigret, Madame: wife in Paris, France by Georges Simenon

Maitland, Anthony: English barrister drawn to murder cases by Sara Woods

Malcolm, Richard: CIA analyst and grad student in Washington D.C. by James Grady

Mallett, Don: thief and poacher in Medwell Fratorum, England by Frank Parish

Mallett, Inspector: in England by Cyril Hare

Mallory: small-town student mystery writer in Iowa by Max Allan Collins

Mallory, Kathleen: NYPD cop in New York, New York by Carol O’Connell

Mallory, Stuart: a private investigator in Lansing, Michigan by Ronald Clair Roat

Malloy, Claire: small-town bookstore owner in Farberville, Arkansas by Joan Hess

Malloy, Hannah: one of an unlikely pair of 60-something sister, in Marine, California by Annie Griffin

Malloy, Laura: a journalist in Minneapolis, Minnesota by Mary Logue

Malloy, Vic: a private investigator in California by James Hadley Chase

Malone, John J.: a lawyer in Chicago, Illinois by Craig Rice

Malone, Scobie: family-man police inspector in Sydney, Australia by Jon Cleary

Malory, Sheila: a writer of literary criticism in Taviscombe, England by Hazel Holt

Man, George: 18th century parish watchman in London, England by Keith Heller

Manchu, Fu: a pursuer of world dominance, by Sax Rohmer

Mancini, Munch: 1970s ex-druggie and jailbird in Los Angeles, California by Barbara Seranella

Mangum, Cuddy: 1/2 of a pair of police detectives in a small town in North Carolina by Michael Malone

Manion, Terry: private eye in New Orleans, Louisiana by Dick Lochte

Mann, Tiger: a spy in New York, New York by Mickey Spillane

Manning, Mark: a gay journalist in Chicago, Illinois by Michael Craft

Mansfield, Patrick: a detective sergeant in Suffolk, England by Ann Quinton

Dr. Manson by Edwin Radford and M. A. Radford

Inspector Manson by Edwin Radford and M. A. Radford

Manwaring, Kevin: field producer in Los Angeles, California by Robert Irvine

Manziuk, Paul: Detective Inspector with homicide, in Toronto, Ontario, Canada by N. J. Lindquist

Mapstone, David: ex-cop, now unemployed college history teacher back in law enforcement, in Phoenix, Arizona by Jon Talton

Mappestone, Sir Geoffrey: a knight during the time of the Crusades by Simon Beaufort

Marcella, Aurelia: a young Roman innkeeper in Roman Britain in 91 AD by Jane Finnis

March, Colonel: head of Scotland Yard's fictitious Department D-3, the Department of Queer Complaints by John Dickson Carr

March, Jasmine: cookbook author and gourmand specializing in rich recipes in Georgetown, Washington D. C. by Nina Killham

March, John by Peter Spiegelman

March, Tobias and Lavinia Lake, lovers and partners-in-crime investigators, in Regency London, England by Amanda Quick

Markby, Inspector Alan: detective inspector in Cotswolds, England by Ann Granger

Markham-Johnson, Helen: actress recruited by the Secret Service in London, England by Eileen Dewhurst

Marklin, Peter: a toyshop owner and antique toy collector in Dorset, England by Neville Steed

Marley, Calista:  forensic pathologist and wife, in Cleveland, Ohio by Bill Pomidor

Marley, Plato: family physician and husband in Cleveland, Ohio by Bill Pomidor

Marlin, John: a game warden in Blanco County, Texas by Ben Rehder

Marlowe, Philip: private eye on the "mean streets" of Los Angeles, California by Raymond Chandler

Marlowe, Philip: private eye on the "mean streets" of Los Angeles, California by Robert B. Parker

Marple, Miss: spinster living in St. Mary's Mead, England by Agatha Christie

Marryat, Stephen: an attorney in England by Margaret Leek

Marsala, Cat: freelance investigative journalist in Chicago, Illinois by Barbara D'Amato

Marsden, Grace: a writer of children's books in a  lovely reclaimed marsh compound called Pine Marsh, Illinois by Luisa Buehler

Marsh, Harry: chief inspector in England by Jo Bannister

Marshall, Neil: graduate student in creative writing, struggling poet and part-time chef and caterer in Houston, Texas by Tim Hemlin

Martens, Harriet: a detective superintendent in Greater Birchester, England by H. R. F. Keating

Martin, Cezanne: a cop in Fort Worth, Texas by Laurie Moore

Martin, Christine: a 40-something cub reporter in England by Annette Roome

Martin, Dorothy: American schoolteacher retired in England by Jeanne M. Dams

Martin, Saz: a lesbian private investigator in London, England by Stella Duffy

Martindale, Thomas: a college journalism professor in Oregon by Ron Lovell

Martinelli, Kate: homicide detective in San Francisco, California by Laurie R. King

Marvelli, Frank: a member of the New Jersey parole violators search team by Anthony Bruno

Marx, Albie: an ex-60s radical and a columnist for a radical magazine in the 90's in Los Angels, California by David Debin

Marx, Groucho: a movie star in Hollywood, California by Ron Goulart

Mary Helen, Sister: retired nun in San Francisco, California by Sister Carol Anne O'Marie

Mason, Perry: defense attorney in Los Angeles, California by Erle Stanley Gardner

Mason, Lou: an attorney in Kansas City, Missouri by Joel Goldman Mason, Tom: a gay teacher in Chicago, Illinois by Mark Richard Zubro

Masters, Molly: cartoonist and greeting card entrepreneur in Albany, New York by Leslie O’Kane

Masterson, Marla: a young British Professor of Anglo Saxon Literature in the United States by Peter Dunant

Masuto, Masao: private investigator in Beverly Hills, California by E.V. Cunningham

Matelli, Angela: an ex-Marine turned private investigator in Boston, Massachusetts by Wendi Lee

Matthews, Charles: a sheriff in Crawford County, Texas by D.R. Meredith

Matthews, Daphne: police psychologist in Seattle, Washington by Ridley Pearson

Matthews, Nell: a newspaper reporter in Grantham, Oklahoma by Eve K. Sandstrom

Alex Mavros: half-Greek, half-Scottish private investigator in Greece by Paul Johnston

Max, Gaston: by Sax Rohmer

Maxim, Harry: Special Services Major, assigned to 10 Downing Street in London, England by Gavin Lyall

Maxwell, Lauren: an investigator for the Wild America Society in Anchorage, Alaska by Elizabeth Quinn

Maxwell, Sgt “Mama”: a detective in future Topeka, Kansas by Lee Killough

Maxwell, Peter: a widowed teacher and golden-hearted cynic in England by M. J. Trow

Maybridge, Tom: a detective chief inspector in England by B. M. Gill

Mayo, Asey: former sailor & auto racer in Cape Cod, Massachusetts by Phoebe Atwood Taylor

Mayo, Gil: a police detective in Midlands, England by Marjorie Eccles

McAfee, Kerry and Terry:   twin fledgling investigators in Southern California by Jennifer Colt

McAvoy, Ed: police chief in Ulster County, New York by Bill Stackhouse

McBride, Rex: a private eye in Los Angeles, California by Cleve F. Adams

McCabe, Cassidy: a psychotherapist and a calico cat in Oak Park, Illinois by Alex Matthews

McCain, Sam: an attorney in Black River Falls, Iowa by Ed Gorman

McCalastar, Sidney Adamson: an attorney in Littleton, Mississippi by Faye Snowden

McCaleb, Terry: retired FBI agent in Los Angeles, California by Michael Connelly

McCandler, Doan: a gay private investigator in San Francisco, California by Orland Outland

McCarron, Blue: independent social psychologist/PI near San Diego, California by Abigail Padgett

McCarthy, Gail: a veterinarian in the Santa Cruz Equine Practice, in Santa Cruz, California by Laura Crum

McCauley, Quint: ex-cop turned private investigator in a Chicago suburb in Illinois by D. C. Brod

McCleary, Mike: part of a wife & husband P.I. team by T. J. MacGregor

McCleet, Adam: ex-cop turned sculptor in Portland, Oregon by Rick Hanson

McClintock, Lara: an antiquities dealer and shop owner in Toronto, Ontario, Canada by Lyn Hamilton

McClintock, Shirley: a 50-something rancher in Colorado by B. J. Oliphant

McCloud: a New Mexico marshal in New York by Collin Wilcox

McCone, Sharon: legal investigator/private eye in San Francisco, California by Marcia Muller

McCool, Doug, a Vietnam vet and process server in San Francisco, California by Miles Archer

McCorkle, "Mac": a saloon owner in Bonn, Germany by Ross Thomas

McCoskey, Sunny: a chef in wine country, Napa Valley, California by Nadia Gordon

McCracken, Blaine: an exiled agent by Jon Land

McCoskey, Sunny: a chef in wine country, Napa Valley, California by Nadia Gordon

McCrite, Carrie: a widow in the Ozark mountains of Arkansas is featured in the Something to Die for Mysteries by Radine Trees Nehring

McCulloch, Mattie: the first female Incident Commander at a major fire site, in Montana by Christine Andreae 

McCutcheon, Claude:   a laid-back bachelor lawyer in the San Francisco-Bay Area, California by John A. Miller

McDougal, James: homicide inspector, in Wingate, Connecticut by Hildegarde Dolson

McCray, James “Mack”: a federal undercover cop in Stuart, Florida by Paul E. McElroy

McFaile, Korine: a landscaper and partner in Three Dirty Women Landscaping, Inc. in Pine Grove by Julie Wray Herman

McFarland, Mac: a burned-out reporter in Cape Cod, Massachusetts by Doug Kiker

McGarr, Peter: police officer in Dublin, Ireland by Bartholomew Gill

McGarvey, Kirk: superspy by David Hagberg

McGee, Travis: adventurer, philosopher and private eye in Fort Lauderdale, Florida by John D. MacDonald

McGrail, Nuala Anne: young Irish immigrant, psychic and singer in Chicago, Illinois by Andrew M. Greeley

McGrogan, Annie: an actor and private investigator in New York City by Gillian B. Farrell

McInnes, Tom: a young attorney in Coopers Bend, Alabama by Mike Stewart

McIntire, John: retired military intelligence officer and newly appointed township constable in St. Adele, Michigan by Kathleen Hills

McIntyre, Ross: small town high school biology teacher in Maine by Kate Clark Flora

McKenzie, Greg: a retired Air Force criminal investigator in Nashville, Tennessee by Chester Campbell

McKall, Sam: a political advisor in Utah by Eric C. Evans

McKenna, Brian: police detective in New York, New York by Dan Mahoney

McKenna, Michael: detective chief inspector (DCI) in Wales by Alison G. Taylor

McKenna, Patience Campbell: 6-ft romance novelist turned crime writer in New York by Jane Haddam

McKenzie, Alex: a doctor in Maine by J. S. Borthwick

McKenzie, Ellie: a newly certified real estate agent returning to her old hometown of Santa Louisa by Kathleen Delaney

McKenzie, Joanna: former CID turned PI in Bath, England by Margaret Duffy

McKinney, Lee: a divorcee, returns to Michigan to work for her aunt's chocolate business by Joanna Carl

McKnight, Alex: a former cop turned rental agent, works on the Michigan's Upper Peninsula, on the shore of Lake Superior by Steve Hamilton

McLeish, John: DCI in London, England by Janet Neel

McMonigle, Judith: bed and breakfast owner in Seattle, Washington by Mary Daheim

McMorrow, Jack: a small-town editor in Androscoggin, Maine by Gerry Boyle

McNally, Arch: playboy private eye in Palm Beach, Florida by Lawrence Sanders

McNally, Arch: playboy private investigator in Palm Beach, Florida by  Vincent Lardo.  Vincent Lardo continued the Arch McNally series after Lawrence Sanders’ death. 

McPherson, Jane: the daughter of an American missionary couple, returns to China after 60 years by Jennifer Scheel Bushman and Jean Artley Szymanski

McTavish, Stoner: a lesbian travel agent in Boston, Massachusetts by Sarah Dreher

McWhinny, Tish: 70-something Vermont artist and painter by B. Comfort

Meade, Lois: cleans houses for pin money in a quaint village named Long Farnden, England by Ann Purser

Meadows, Jayne: celebrity crime-solver in Los Angeles, California by Steve Allen

Medina, John: a CIA agent by Linda Howard

The Medieval Mystery Series by Alan Gordon

Meiklejohn, Charlie: ex-arson investigator P.I. in New York by Kate Wilhelm

Men at War Series: featuring the OSS during World War II by W. E. B. Griffin

Mendoza, Luis: lieutenant in the Los Angeles Police Department in California by Dell Shannon

Menlo, Anne: a child psychologist in Phoenix, Arizona by Maxine O'Callaghan

Mercer, Philip: an engineer, geologist and eco-warrior by Jack Du Brul

Meren, Lord: chief investigator for Pharaoh Tutankhamen in Egypt by Lynda S. Robinson

Merlin, Jack: a surgeon and magician in Pittsburgh, Pennsylvania by James Tucker

The Great Merlini;  a stage magician by Clayton Rawson

Merrick, Michael: a newspaperman in 1840s Boston, Massachusetts by Mary Jo Adamson

Merrivale, Sir Henry: holder of one of the oldest baronetcies in England, physician, barrister, head of military intelligence for the war office in England by John Dickson Carr

Metellus, Decius Cecilius: would-be playboy son of an illustrious family, is featured in the SPQR historical mysteries by John Maddox Roberts

Michaels, Laura: a retirement center social worker in Timberlake, Oklahoma by John Miles

Michaelson, Richard: is a retired diplomat with the Foreign Service Office in Washington D. C. by Michael Bowen

Middleton-Brown, David: solicitor in London, England by Kate Charles

Mikaelian, Garreth: vampire cop, first in San Francisco, California and later in Baumen, Kansas by Lee Killough

Miller: bicycling enthusiast and reporter, transferred from Belfast to Crossmaheart, Northern Ireland by Colin Bateman

Miller, Hannah (Granny Hanny), a mystery reader and quilt-making enthusiast, in Pennsylvania, in the Amish Country mysteries by Barbara Workinger

Miller, Lydia: 30-something fashion editor in New York, New York by Eleanor Hyde

Miller, Nick: Sgt. Central Division detective in London, England by Jack Higgins

Millholland, Kate: an attorney in Chicago, Illinois by Gini Hartzmark

Millhone, Kinsey: private eye in Santa Teresa, California by Sue Grafton

Mills, Todd: a gay TV news reporter in Minneapolis, Minnesota by R. D. Zimmerman

Milodragovitch, Milo: ex-Army spy and hard drinking private investigator in Montana by James Crumley

Milano, John: a private investigator by Stanley Ellin

Minogue, Matt: a sergeant in the Irish police detective in Dublin, Ireland by John Brady

Miracle, Tori: ex-New York City crime writer turned Pennsylvania novelist by Valerie Malmont

Mitchell, Meredith: Foreign Service officer in Cotswolds, England by Ann Granger

Mitchell, Benny: a brash detective constable in Cloughton, Yorkshire, England by Pauline Bell

Mitchell, Michelle “Mitch”: a deep-sea diver and bar owner in Huron Harbor, Michigan by Doug Allyn

Mitchell, Scott: private investigator in England by John Harvey

Mom, Dave's mother, in Mesa Grande, Colorado by James Yaffee

Monaghan, Tess: private investigator in Baltimore, Maryland by Laura Lippman

Monarch, Greg: a lawyer in La Graciosa, California by Barry Siegel

Monk, Dittany Henbit: a garden club member in Lobelia Falls, Ontario, Canada by Alisa Craig

Monk, Osbert: author and husband in Lobelia Falls, Ontario, Canada by Alisa Craig

Monk, Inspector William: amnesiac Victorian police inspector by Anne Perry

Monks, Carroll: an emergency-room doctor in San Francisco, California by Neil McMahon

Monkeyman, Dave the: sidekick and ASL signer for the president of a large security firm in Miami, Florida by Hialeah Jackson

Monroe, Louis: a Don Quixote-style cop, in Atlantic City, New Jersey by Bill Kent

Montalbano, Salvo: a police inspector in Sicily by Andrea Camilleri

Montana, Lane: a finder of lost things, in Atlanta, Georgia by Kay Hooper

Montero, Britt: newspaper crime reporter in Miami, Florida by Edna Buchanan

Montez, Luis: an attorney and former Chicano activist in Denver, Colorado by Manuel Ramos

Montford, Suzie: a Woman Police Constable in London, England during the Blitz by John Gardner

Montgomery, Grant: a 40-something retired mentalist and entertainer in Pittsburgh, Pennsylvania by Robert Aiello

Montrose, Bridget: a mother of small children in Palo Alto, California by Lora Roberts

Montrose, Claire: an amateur sleuth in Oregon by April Henry

Montrose, Jean: physician in Scotland by C. F. Roe

Moodrow, Stanley: a cop turned private eye in New York, New York by Stephen Solomita

Moon, Charlie: Ute police officer in Grant Creek, Colorado by James Doss

Moon, Louise: a mortuary technician at Charity's (The Charitable Hospital of St. Roche Without the Walls) mortuary, in London, England by Anne Morgellyn

Moon, Phyllida: television private eye in London, England by Eileen Dewhurst

Moore, John Schuyler: turn-of-the-century journalist in New York, New York by Caleb Carr

Moore, Rebecca: a reporter by Judith Skillings

Morales, Mira: a bookstore owner and psychic, in Tango Key, Florida by T.J. MacGregor

Morell, Charlie: a Cuban-American private investigator turned lawyer in Los Angeles, California by Alex Abella

Morgan, Dexter: is a blood spatter technician for Miami Dade Police Department.  He is also a sociopathic serial killer by Jeff Lindsay

Morgan, Rain: newspaper reporter in London, England by Lesley Grant-Adamson

Morgan, Taylor: medi-flight pilot in Alaska by Megan Mallory Rust

Moriarty, Professor: archenemy of Sherlock Holmes in London, England by John Gardner

Morrelli, Nick: a sheriff in Platte City, Nebraska by Alex Kava

Morelli, Teddy: college history professor in Seattle Washington by Linda French

Morrissey, John: a chief inspector and family man in Malminster, England by Kay Mitchell

Morse, Chief Inspector: inspector  in Oxford, England by Colin Dexter

Moseley, Hoke: a cop in Miami, Florida by Charles Willeford

Moses, Zen: a private investigator and cancer survivor in Santa Monica, California by Elizabeth Cosin

Mosley, Inspector: an inspector in the Lancashire and Yorkshire border country in England, written as John Greenwood

Moss, Phil: a Scottish Crime Squad officer in Glasgow, Scotland by Bill Knox

Moss, Wiley: graphic artist in Washington D.C. by Neal Barrett Jr.

Mr. Moto, a Japanese secret agent John P. Marquand

Mott, Angus: a police sergeant in Thames Valley, England by Clare Curzon

Mostyn, Colonel: by Mark Hebden

Mulcahaney, Norah: homicide detective in New York, New York by Lillian O'Donnell

Mulcay, Kate Kincaid: veteran newspaperwoman in Atlanta, Georgia by Celestine Sibley

Muldoon, half of a pair turn-of-the-century policemen in New York, New York by William Marshall

Mulheisen, “Fang”,  police detective in Detroit, Michigan by Jon A. Jackson

Munro, Dougal: 1940s brigadier in Ireland by Jack Higgins

Murdoch, William: private investigator in 1890s Toronto, Ontario, Canada by Maureen Jennings

Murphy, Jack: an ex-cop turned private investigator in Los Angeles, California by David J. Sherman

Murphy, Molly: a Irish immigrant in 19th-century New York, New York by Rhys Bowen

Musing, Hiawatha and Antigone: siblings, professors, and part-time sleuths, are featured in the Ivory Tower mysteries by David D. Nolta