The Door with Seven Locks

This West German production is the second film based on the Edgar Wallace novel of the same name (the first was the 1940 Chamber of Horrors). The story -- which owes a great deal to The Cat and the Canary -- concerns the potential heirs to an eccentric's fortune, whose potential wealth (and fate) is tied to the acquisition of seven keys that will purportedly unlock a secret treasure vault. When the heirs begin turning up dead with said keys in their possession, a Scotland Yard inspector (Heinz Drache) attempts to assemble the puzzle. Things are further complicated by a series of abductions involving a sadistic mad scientist and his diabolical experiments.