An ancient Chinese artifact has been stolen by a villainous archaeologist named Dexter. With the help of his Lemming friends, Norm must keep his word and embark on a journey across the world to help recover the artifact for the people of China.

Norm and his oldest son travel back to New York to receive the key to the city.

When Earth astronaut Capt. Chuck Baker arrives on Planet 51 — a world reminiscent of American suburbia circa 1950 — he tries to avoid capture, recover his spaceship and make it home safely, all with the help of an empathetic little green being.