Having literally gone from rags to riches, Alvin, Simon and Theodore didn't think their lives could get any better - and they certainly didn't think it could all go downhill. Their best friend and father figure Dave has met a woman, and while the chipmunks are happy to have a new face in their lives, they're super worried it could mean the end for them. Dave is going to Miami to propose and is planning on leaving his furry friends at home in Los Angeles. But after a serious misunderstanding, the guys believe that they are going to be abandoned forever. And so, they set out follow Dave to the sunny city to stop the proposal and save their friendship with Dave - while gaining yet more fans with their spontaneous musical exhibitions along the way.
Alvin, Simon and Theodore are preparing to embark on more mischievous adventures; venturing out on a road trip to New York, throwing star-studded parties and doing what they love best - singing! But meanwhile, they have some serious business to attend to. They are convinced that their friend Dave is planning on proposing to his girlfriend, before leaving the chipmunks to fend for themselves. It's all a huge misunderstanding, of course, but these musical rodents have a good reason to believe they might lose their buddy; it's not as if they make life easy for him. Thus, the chipmunks - led by Alvin - set out to travel cross country to meet Dave in New York and convince him not to propose. Not only are they worried about being left alone, but they're also not loving the idea of their potential new stepbrother.