When Dennis finds Professor Screwtop's time machine in the lab, he can't resist using it without reading the instructions, and starts a chain of events that lead to Gnashersaurus rex's rampaging through Beanotown! How is Dennis going to set things right without bumping into other versions of himself and destroying the space time continuum!

When the gang's sausages go missing, and they discover gnashed bicycle wheels and one of Gnasher's teeth, it seems like there's only one suspect. But Dennis refuses to believe that Gnasher is to blame. Gnasher realizes he's being set up by Clawdia, Walter's ultra sneaky cat, and has to find a way to prove his innocence.