International criminal Jacques Müller (Klaus Kinski) and his girlfriend Louise Andrews (Susan George) plan to kidnap Philip Hopkins (Lance Holcomb), the grandson of Howard Anderson (Sterling Hayden), a retired hunter and the wealthy owner of a hotel chain. Louise goes undercover as a maid working for Philip's mother Ruth and seduces her chauffeur Dave Averconnelly (Oliver Reed), convincing him to help in the kidnapping. On the day of the kidnapping, Müller tricks Howard and Ruth into leaving home while Louise and Dave kidnap the boy. Philip leaves briefly to retrieve a pet snake, which is accidentally swapped with a black mamba meant for toxicologist Dr. Marion Stowe. Howard returns home early, and the black mamba is released and bites Louise in the face repeatedly before fleeing into the ventilation system.