Jerry Lewis is Kreton, a childish alien who, against his teacher's will leaves his planet to visit the Earth, and lands in the backyard of a famous television journalist who doesn't believe in U.F.O's and aliens. Wanting to study humans but not able to fully understand them, Kreton makes a mess out of it, generating a lot of comic situations.

In New York, the interior decorator Jan Morrow and the wolf composer Brad Allen share a party line, but Brad keeps it busy most of the time flirting with his girlfriends. They do not know each other but Jan hates Brads since she needs the telephone for her business and can not use it. Coincidently Jan's wealthy client Jonathan Forbes that woos her is the best friend of Brad and he comments with him that he feels an unrequited love for Jan, who is a gorgeous woman. When Brad meets Jan by chance in a restaurant, he poses as a naive tourist from Texas named Rex Stetson and seduces her. But Jonathan hires a private eye to find who Rex Stetson is.

Molly and Terry Donahue, plus their three children, are The Five Donahues. Son Tim meets hat-check girl Vicky and the family act begins to fall apart.

Cagney is Danny Kenny, a truck driver who enters "the fight game" and Sheridan plays his girlfriend...