Books about Detective and mystery stories (sorted alphabetically)
- Opal Serpent Fergus Hume
- Orange-Yellow Diamond J. S. Fletcher
- Oscar the Detective; Or, Dudie Dunne, The Exquisite Detective Old Sleuth
- Other Man Edgar Wallace
- Other People's Money Emile Gaboriau
- Out of a Labyrinth Lawrence L. Lynch
- Out of Death's Shadow; Or, A Case Without a Precedent Nicholas Carter
- Owen Clancy's Happy Trail; Or, The Motor Wizard in California Burt L. Standish
- Owl Taxi Hulbert Footner
- Oxbow Wizard Theodore Goodridge Roberts
- Pagan's Cup Fergus Hume
- Panther Eye Roy J. Snell
- Paradise Mystery J. S. Fletcher
- Paradise Mystery J. S. Fletcher
- parfum de la Dame en noir (French) Gaston Leroux
- Passenger from Calais Arthur Griffiths
- Paternoster Ruby Charles Edmonds Walk
- Patty's Friends Carolyn Wells
- Pawns Count E. Phillips Oppenheim
- Peacock of Jewels Fergus Hume
- Peli elämästä ja kuolemasta: Salapoliisikertomus (Finnish) Sven Elvestad
- Pelikello: Salapoliisikertomus (Finnish) Sven Elvestad
- Penny Nichols and the Black Imp Joan Clark
- Penny Nichols and the Knob Hill Mystery Joan Clark
- Penny Nichols and the Mystery of the Lost Key Joan Clark