 Martin needs to lose 3 pounds to be able to fly his weight sensitive spaceship properly. Luckily he has a machine that can collapse the necessary 3 pounds of fat molecules from his body. However, Tim presses the wrong switch and instead shrinks the spaceship to toy size. Fortunately the ship will expand back to its normal size in time, the "when" being the question. While Martin is gone on an errand and Tim unavoidably detained, a dog comes by and takes off with the ship. They find the dog, who tells them that their master is a Jolly Toys executive who has patented the design of the new "boomerang spaceship". Tim and Martin go down to his office to steal the ship, and think they do so, except it ends up being an actual toy. The real ship has an "A-flat" sound sensor which ll help Martin find it among all the mass produced ships in the factory. Unable to find it in the shipping department, they find out that it was in another shipment already gone to a department store. Martin and Tim get to the store just in time to fight a precocious child, his permissive mother and a tough-as-nails sales clerk, for the real ship, which is growing in the child s hands. After they wrestle it away, Martin and Tim have one last obstacle - how to get the growing spaceship home without being obvious.