Nick Daley is following in his father's footsteps as night watchman at the American Museum of Natural History, so he knows what happens when the sun goes down. But when the maniacal ruler Kahmunrah escapes, it is up to Nick to save the museum once and for all.
A group of strangers come across a man dying after a car crash who proceeds to tell them about the $350,000 he buried in California. What follows is the madcap adventures of those strangers as each attempts to claim the prize for himself.
Disgraced and cast out of his tribe for lusting after Lana, the mate of the tribe's head muscle man, Atouk stumbles along gathering other misfits and learning a bit about the world outside of his cave. Eventually he and friends Lar and Tala learn the secrets of fire, cooked meat, and how to defend themselves from the brutal, yet very stupid dinosaurs.
Two rich children devise a way to escape their grandfather and visit their mother. Unfortunately for two hapless safe crackers, they become part of the plan.