A serial killer terrorizes London. Each victim is found with a telegram signed "The Marquis." There seems to be no other common thread between the victims, and Scotland Yard is baffled. Novelist and amateur sleuth, Paul Temple, is warned to stay away from the case, but he and his glamorous wife Steve can never refuse a good mystery.
| Actor | Role |
|---|---|
 John BentleyPaul Temple | Paul Temple |
 Patricia DaintonSteve Temple | Steve Temple |
 Peter GawthorneSir Graham Forbes | Sir Graham Forbes |
 Valentine DyallBradley | Bradley |
 Ronald Leigh-HuntInspector Ross | Inspector Ross |
 Grey BlakeStorey | Storey |
 Dan JacksonSakki the Valet | Sakki the Valet |
| BBen WilliamsRoddy Carson | Roddy Carson |
 Robert UrquhartSlater | Slater |
 Christopher LeeSir Felix Raybourne | Sir Felix Raybourne |
| GGeorge PattersonServant Abdullah | Servant Abdullah |
 Michael MulcasterSir Graham's Police Aide | Sir Graham's Police Aide |
 Andreas MalandrinosSammy Wren | Sammy Wren |
| MMargaret SamuelRita Cartwright | Rita Cartwright |
| EElizabeth GilbertBarmaid | Barmaid |
 Vi KaleyOld 'Em | Old 'Em |
| GGerald RexRifle-range Attendant | Rifle-range Attendant |
| Michael MulcasterPolice Sergeant | Police Sergeant |
| SSylvia PughSecretary | Secretary |
| DDenis HolmesMobile Policeman | Mobile Policeman |
| JJohn AdamsPolice Constable | Police Constable |
| JJoe WadhamPinball Machine Player | Pinball Machine Player |