Wealthy Mr. Kennedy shoots his secretary, Channing, during a parlor game, but it turns out the gun was loaded with real bullets. Luckily, criminologist Phillip Montrose is on hand to help the police. When Kennedy quickly ends up dead as well, the police think it's a tidy murder-suicide, but the family lawyer knows of a letter that voiced Kennedy's suspicions about someone who was out to get him. Soon, the cops are on the trail of a ruthless and clever killer who is one step ahead of even Montrose.

Esther Clay, wife of District Attorney John Clay and mother of attorney Bob Clay, is having an affair with Jack Keene. Scorned by him Esther kills Jack. Bob comes to her defense and confesses to the shooting. The father prosecutes the son who receives a life imprisonment sentence. Jack Keene's butler Druggett knows the truth and blackmails Esther. Bob's girlfriend Peg Harper summons John Clay to the scene...

Ruth Earlton has come home to her ancestral mansion to claim her inheritance. Accompanied by her boyfriend, she discovers that her father died suddenly under suspicious circumstances. Now it's her turn, as her deranged and relentless uncle targets her for death with the help of his wife and son, plus a very unhappy ape.

When the villagers of Klineschloss start dying of blood loss, the town fathers suspect a resurgence of vampirism. While police inspector Karl remains skeptical, scientist Dr. von Niemann cares for the vampire's victims one by one, and suspicion falls on simple-minded Herman Gleib because of his fondness for bats. A blood-thirsty mob hounds Gleib to his death, but the vampire attacks don't stop.