Michael Lanyard is suspected of stealing two fabulous diamonds from a vault in Scotland Yard, where they were being held for safekeeping, but the Yard can't prove he did it. Later, Lanyard is summoned by a member of the nobility to help the latter raise money to pay a blackmailer. Lanyard later finds evidence to reveal the diamonds as having been stolen by a famous stage star.

The stooges hope to collect a reward by proving to a museum that cavemen still exist. They return from their expedition with a film purporting to show some stone age stooges defending their women from other cavemen. The museum curators are about to pay they reward, until they overhear the stooges talking about how they faked the film, with themselves playing the cavemen.

Set in the stone age, the stooges are cavemen who must have various misadventures hunting, gathering, and otherwise coping with prehistoric life. When some other cavemen threaten to take their women ("Aggie", "Maggie", and "Baggy"), the boys fight them off with a catapulting tree branch that shoots rocks and eggs.