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 reckless janitor accidentally releases a zombie from a laboratory of research. Meanwhile, the teenagers scouts Ben Goudy and Carter Grant decide to camp for the last time since they are too old to be scouts. The problem is that they do not want to harm the feelings of their friend Augie Foster and the Scout Leader Rogers. They have a flat tire after hitting a deer on the road and Carter's sister Kendall Grant, her boyfriend and her friend Chloe stop their Jeep to see whether they need a ride....

An extremely wealthy man, dying from cancer, undergoes a radical medical procedure that transfers his consciousness into the body of a healthy young man. But all is not as it seems when he starts to uncover the mystery of the body's origin and the organization that will kill to protect its cause.