Dennis Quaid stars as a rambunctious Navy test pilot undergoes a top-secret miniaturization experiment and is accidentally injected into the body of a hypochondriac clerk (Martin Short).

A scientifically miniaturized marine unexpectedly finds himself floating around the body of a hypochondriac, and trying to outwit saboteurs who want the device that shrank him.

Attempts by his colleagues to retrieve the little man - protected inside a tiny submersible - are hampered by the would-be thieves.