The tree that the chipmunks Alvin (Justin Long), Simon (Matthew Gray Gubler) and Theodore (Jesse McCartney) live in is cut down and driven to Los Angeles. Once in L.A., the Chipmunks meet struggling songwriter David Seville (Jason Lee) who had his latest song rejected by JETT Records executive Ian Hawke (David Cross), his old college roommate. Dave also once had a relationship with his next door neighbor, Claire Wilson (Cameron Richardson).

After winding up at Dave’s interview, the Chipmunks hop into his basket and follow him home. Once at home, Dave discovers the Chipmunks, and is accidentally knocked unconscious. Upon waking, he kicks them out until hearing them sing “Only You (And You Alone)”. Dave then makes a deal with them; they sing the songs he writes, and Dave’s also a former boss Gail (Jane Lynch) in exchange he provides food and shelter for them…