Plucky doesn't have his homework done, so he decides to build a time machine to go back and do it. He's saved the trouble when a future version of Plucky comes with a time machine. Future Plucky and Plucky go back to when Plucky got the homework. Plucky takes the time machine, leaving Future Plucky to do the homework. Plucky goes back in time with Buster and Babs, who wind up somewhere in time while Plucky goes to prehistoric times. Eventually, Buster and Babs find Plucky, and Plucky goes to his time, bringing a prehistoric monster with him and leaving Buster and Babs behind. And so, Buster and Babs are stuck in the past until Plucky swaps the prehistoric monster for Buster and Babs. After all that, Plucky's homework still isn't done, as Future Plucky sure wasn't gonna do it...