A young teenager named Mikey Walsh finds an old treasure map in his father's attic. Hoping to save their homes from demolition, Mikey and his friends Data Wang, Chunk Cohen, and Mouth Devereaux run off on a big quest to find the secret stash of Pirate One-Eyed Willie.

An expedition into the interior of Papua New Guinea comes across a tribe of ape-like people who may or may not be ancestors of early man.