A struggling songwriter named Dave Seville finds success when he comes across a trio of singing chipmunks: mischievous leader Alvin, brainy Simon, and chubby, impressionable Theodore.

Pop sensations Alvin, Simon and Theodore end up in the care of Dave Seville's twenty-something nephew Toby. The boys must put aside music super stardom to return to school, and are tasked with saving the school's music program by winning the $25,000 prize in a battle of the bands. But the Chipmunks unexpectedly meet their match in three singing chipmunks known as The Chipettes - Brittany, Eleanor and Jeanette. Romantic and musical sparks are ignited when the Chipmunks and Chipettes square off.

Through a series of misunderstandings, Alvin, Simon and Theodore come to believe that Dave is going to propose to his new girlfriend in New York City - and dump them. They have three days to get to him and stop the proposal.

Playing around while aboard a cruise ship, the Chipmunks and Chipettes accidentally go overboard and end up marooned in a tropical paradise. They discover their new turf is not as deserted as it seems.