Detective Lou  Cagell is a fighter of crime on the waterfront. He is on a ship back from Bermuda to New York when the captain of the ship asks him for his help to protect one of the passengers from being kidnapped, Yes kidnapped on a ship. The young lady is wealthy heiress Helena Dawson. Once she is on board the ship she finds a note in her vanity case telling her telling her if she doesn't pay up $10,000 she will not leave the boat alive. Lou Cagell is the only passenger on board experienced in police work so agrees to help Miss Dawson.