When one of the Smurfs wants to travel to outer space, he tries to build a rocket ship, but it fails to get off the ground and he grows depressed. Papa Smurf and the other Smurfs make a plan in order to cheer him up: putting him to sleep and waking him up in an elaborately staged "planet" filled by other Smurfs pretending to be aliens. Hilarity ensues when their elaborate hoax proves to be more trouble to keep up than it's worth!