Professor Moriarty series

• The Infernal Device (1978); reprinted in The Infernal Device and others
• Death by Gaslight (1982); reprinted in The Infernal Device and others
• "The Paradol Paradox" (in The Infernal Device and others, 2001)
• The Great Game (2001)
• "Years Ago and in a Different Place" (in My Sherlock Holmes, 2003)
• "Reichenbach" (in Sherlock Holmes: The Hidden Years, 2004)
• The Empress of India (2006)

Lord Darcy series

• Ten Little Wizards (1988)
• A Study in Sorcery (1989)

Alexander Brass series

• Too Soon Dead
• The Girls in the High-Heeled Shoes
• "He Couldn't Fly" (in The Mammoth Book of Roaring Twenties Whodunnits)

War Incorporated series

• Mission: Third Force
• Mission: Tank War
• A Plague of Spies

Science fiction

• Ten Years to Doomsday (with Chester Anderson) (1964)
• The Unicorn Girl (1969)
• Transmission Error (1970)
• Pluribus (1975)
• The Whenabouts of Burr (1975)
• Tomorrow Knight (1976)
• The Princes of Earth (Young Adult) (1978)
• The Last President (S. W. Barton) (1980)
• Psi Hunt (1980)
• First Cycle (posthumous editing and expanding of a manuscript by H. Beam Piper) (1982)
• Star Griffin (1987)
• Perchance (1989)
• Button Bright (1990)

Anthologies (as editor)

• My Sherlock Holmes: Untold Stories of the Great Detective (2003)
• Sherlock Holmes: The Hidden Years (2004)
• Sherlock Holmes: The American Years (2010)

Short stories

• "Elementary" (with Laurence M. Janifer) (1964)
• "Bond of Brothers" (1965)
• "Please State My Business" (1965)
• "Fimbulsommer" (with Randall Garrett) (1970)
• "Small World" (1973)
• "Think Only This of Me" (1973)
• "A Brief Dance to the Music of the Spheres" (1983)
• "In the Blood" (1995)
• "The Rite Stuff" (2004)
• "Four Hundred Slaves" (2005)

Nonfiction

• The Spymaster's Handbook (1988)
• A Gallery of Rogues: Portraits in True Crime (1994)
• How to Solve a Murder: The Forensic Handbook (1995)
• How to Try a Murder: The Handbook for Armchair Lawyers (1997)
• Irrefutable Evidence -- Adventures in the History of Forensic Science (2009)