Kreton (Jerry Lewis) is an extraterrestrials in fiction who is fascinated by human beings. Against the wishes of his teacher, he repeatedly visits Earth. During his latest visit, his teacher reluctantly agrees to allow him to stay and study the humans. Kreton becomes friends with a suburban family and stays with them after they agree to keep his alien status a secret. Along the way, he falls in love with their daughter (Joan Blackman). However, there is a force shield around him that prevents any physical contact. His race has abolished any form of affection.