A secret, high-technology international agency called SHADO defends Earth from alien invaders.

The assistant stage manager of a small-time theatrical company (Polly Browne) is forced to understudy for the leading lady (Rita) at a matinée performance at which an illustrious Hollywood director (Cecil B. DeThrill) is in the audience scouting for actors to be in his latest “all-talking, all-dancing, all-singing” extravaganza.