When Heather and Wally's parents inform the two that they are expecting guests from out-of-town, they must hide Denver that the local movie theater, which is believed to be haunted.

A boy genius, Freddy Facknitts, invents a time machine that sends Denver and Morton Fizzback into the past and into the middle of a crazy caveman competition called Mammothball.

When disreputable treasure hunters kidnap a valuable dolphin from a marine research facility and use him to locate sunken treasure, Denver dives in to save the dolphin.

Denver and Mario take a job as children's entertainers only to incur the wrath of Douggie, the Dancing Clown, who tries to sabotage Denver and Mario's entertaining efforts.