A man and wife are terrorized by Mad Scientist Dr. Callistratus who was executed but has returned to life with a heart transplant. Along with his crippled assistant Carl, the 'anemic' Mad Scientist, believed to be a vampire, conducts blood deficiency research on the inmates of a prison hospital for the criminally insane to sustain his return to life.
| Actor | Role |
|---|---|
 Donald WolfitDoctor Callistratus | Doctor Callistratus |
 Vincent BallDr. John Pierre | Dr. John Pierre |
 Barbara ShelleyMadeleine Duval | Madeleine Duval |
 Victor MaddernCarl | Carl |
| WWilliam DevlinKurt Urach | Kurt Urach |
 Andrew FauldsChief Guard Wetzler | Chief Guard Wetzler |
 John Le MesurierChief Justice | Chief Justice |
 Bryan ColemanMonsieur Auron | Monsieur Auron |
 Cameron HallDrunken Doctor | Drunken Doctor |
 George MurcellFirst Guard | First Guard |
| JJulian StrangeSecond Guard | Second Guard |
| BBruce WightmanThird Guard | Third Guard |
| BBarbara BurkeHousekeeper | Housekeeper |
 Bernard BresslawTall Sneak Thief | Tall Sneak Thief |
 Hal OsmondSmall Sneak Thief | Small Sneak Thief |
 Milton ReidExecutioner | Executioner |
 Patricia PhoenixWoman | Woman |
| JJack CarterMan in Court (uncredited) | Man in Court (uncredited) |