Sickan, the leader of the criminal Jönsson gang is incarcerated in a mental institution, attended by Dr M.A. Busé, who admire a handbook in crime that Sickan has been writing. Blackmailed by the nefarious banker Wall-Enberg, Dr Busé and Sickan's partners Vanheden and Dynamite-Harry execute Sickan's plan of stealing the valuable Black Diamond of the Romanovs from the National Museum.
| Actor | Role |
|---|---|
 Ulf BrunnbergRagnar Vanheden | Ragnar Vanheden |
 Björn GustafsonDynamit-Harry | Dynamit-Harry |
 Peter HaberDr. Max Adrian Busé | Dr. Max Adrian Busé |
 Birgitta AnderssonDoris | Doris |
 Elias RingquistLillis | Lillis |
 Björn GranathLohman | Lohman |
 Pontus GustafssonAndersson | Andersson |
 Bernt LindqvistThe Chief of Police | The Chief of Police |
 Per GrundénWall-Enberg | Wall-Enberg |
 Weiron HolmbergBiffen Johansson | Biffen Johansson |
 Lena T. HanssonBusé's secretary | Busé's secretary |
 Rikard WolffCount Romanoff | Count Romanoff |
| TThomas SegerströmGuard | Guard |
 Jonas UddenmyrGuard | Guard |
| KKarl Erik AndersenJailer | Jailer |
| UUlf ErikssonPatient | Patient |
| SSten HellströmPatient | Patient |
 Jan MybrandKeeper | Keeper |
| KKjell-Hugo GrandinNot listed | Not listed |
 Ulf FribergNot listed | Not listed |
 Suzanne ErnrupNot listed | Not listed |
| MMarianne KarlbeckNot listed | Not listed |