In this thriller, a small-boat captain, operating off the English coast, gets into trouble when he is hired by an enigmatic foreigner who pays him a great amount of cash to be taken to Holland. On the voyage, the man dies. When he examines the mans corpse, the captain finds an odd map. Upon arrival in Holland, the captain discovers a woman searching the cabin. The girl claims to be the deceased's daughter, but then runs off. Not long after, the boatman learns that the man was an investigator searching for a fortune in treasure stolen by the Nazis and hidden in Holland. The curious man begins investigating the mystery himself. He first finds the man's real daughter and gets her help. Just as they find a large cache of diamonds, the Nazis, who have been trailing them all along, show up and corner them. Fortunately, the Dutch police have been following the Nazis. They show up in the nick of time and justice is served.