In San Francisco, detective partners Jack Packard and Doc Long are hired by socialite Jefferson Monk who believes someone is following him with the aim to kill him.
Down-on-his-luck Mike Cormack is hired to fly to a Caribbean island to retrieve a missing ruby. On the island, possibly involved with the ruby's disappearance, is his ex-girlfriend.
In this musical-comedy, Dean Martin plays an American hotel mogul who becomes smitten with a young Italian woman (Anna Maria Alberghetti) when buying a hotel in Rome. To marry this gal, he has to get her three older sisters married off.
A mysterious hypnotist is suspected by the police of being responsible for a wave of young, attractive women committing various forms of self-mutilation.
