Big-game hunter and wealthy zoologist Eric Gorman (Lionel Atwill) is an insanely jealous husband who uses his animal knowledge to dispose of his impulsive wife's lovers. The film opens in an Indian jungle with Gorman using a needle and thread to sew a colleague's mouth closed after having discovered that he had kissed his wife, and then he seals the man's fate by abandoning him in the jungle with the wild beasts. Gorman later pretends to be surprised at hearing that the man had been eaten by tigers. Both Gorman and his wife Evelyn (Kathleen Burke) then return to America aboard a ship packed with captured animals he intends to add to his collection at a major zoo. On the ship, Evelyn has a relationship with Roger Hewitt (John Lodge), which she tries to hide from her husband. Naturally, the murderously jealous Gorman finds out. Once back in the States, he begins to plot a way to get rid of Hewitt.

The zoo is beginning to run into financial trouble and the new press agent, Peter Yates (Charles Ruggles), a man terrified of most of the zoo's animals and considered to be an alcoholic, suggests hosting a fundraising dinner for the rich to raise funds and awareness. The last straw is when Gorman finds his wife at Hewitt's apartment where they have been plotting their escape and her divorce. Gorman invites Hewitt to the dinner and uses it as the perfect opportunity to dispense his vengeance by poisoning Hewitt with mamba venom. He had obtained the poison after asking the zoo's laboratory doctor, Jack Woodford (Randolph Scott), to work on finding an antitoxin for the snake's fatal bite.

When Hewitt unexpectedly dies at the fundraising dinner, Evelyn accuses her husband of being the murderer. Outraged, Gorman attacks her, but she is able to escape into his office where she finds a mechanical mamba head seeping with real mamba poison in his desk. She now knows for a fact that he killed Hewitt and takes the snake head with the intention to find Dr. Woodford. However, Gorman finds his wife, swears he did everything because he loves her, and prevents her from revealing his crime by throwing her to the alligators, where she is torn to shreds.

Dr. Woodford then becomes suspicious and accuses Gorman of murdering both his wife and Rodger Hewitt. Gorman disposes of Dr. Woodford by attacking him with the mechanical snake head just as he had done to Hewitt. The doctor's assistant Jerry (Gail Patrick) gives Woodford a shot of the antitoxin he had created for the mamba poison in time to save his life. She also realizes that Gorman is responsible for the apparent mamba attack when he tries to stop her, and has the zoo's alarms set off. A police chase ensues as Gorman is pursued through the zoo. Gorman releases big cats from the carnivore house in the hopes of keep back the police, but it backfires and a group of them chases Gorman, and forces him into the cage of a boa constrictor, who then slowly kills and devours him.