Through a series of misunderstandings, Alvin, Simon, and Theodore come to believe that Dave is going to propose to his new girlfriend in Miami, and dump them. They have three days to get to him and stop the proposal, saving themselves not only from losing Dave but possibly from gaining a terrible stepbrother.

A traveling businessman is menaced on the highway by a huge diesel truck. Although he can never see the psychopathic driver of the truck, he soon realizes that this guy is out to kill him!