Robert Griffin (Jon Hall (actor)) is nothing but a mad, psychopathic killer who should be locked away for good. Still he manages to escape from the secluded Cape Town mental institution where he has been committed, and now he is looking for revenge on the respectable Herrick family. A family consisting of Sir Jasper and lady Irene, and their daughter Julie, who are engaged in entertaining, and inspecting, Julie's new boyfriend, newspaper journalist Mark Foster, in the family residence. Later that night Julie and Mark leave the residence together, and Sir Jasper and lady Irene are left alone. That's when Robert decides to pay the couple a visit. Quite unexpectedly he enters the residence and accuses the couple of leaving him to die out in the African wild, injured, when they were on a safari together. The Herrick couple defends themselves, claiming they were told that he was dead and not injured, but Robert doesn't buy their explanation. He demands they give him his share of the diamond fields they all discovered together on the safari. Jasper tries to tell Robert that the diamond fields were all lost in a series of bad investments.