Charles Madigan visits Alice, to tell her that her father died in an accident while the two professional treasure hunters were diving at the coast of Gibraltar. Whilst practicing, Madigan finds a car wreck underwater with recently stolen diamonds in it, which he keeps. This gets him the attention of the gangster Arman Campana and finally lets him find out the truth about his friend's death. He tries to win police officer Paul Valence - who's competing with him for Alice's love - to help him use ...