Lt. Tuck Pendleton (Dennis Quaid), a former Air Force pilot, volunteers to be miniaturized with the help of two experimental microchips. But as techno-thieves steal one of them, he is injected into supermarket clerk Jack Putter (Martin Short). Now they must find the missing chip with the help of Tuck's ex-girlfriend, Lydia (Meg Ryan), before the air supply in the pod that Tuck is piloting around inside Jack's body runs out.