The Great Lover (1949) on Netflix

The French Surete and private eye Higgins are after a killer who uses innocent young Americans in a crooked gambling racket, and who sets sail on an ocean liner that also carries inept scoutmaster Freddie Hunter and his troop of boys. Freddie, who's been a "boy scout" too long, has designs on gorgeous Duchess Alexandria. The boys, far better organized than Freddie, are determined to save him from himself. But who will save Freddie from being the killer's next victim?