Ship captain Duncan is found murdered, his pockets stuffed with counterfeit money. It is presumed that Duncan was planning to distribute the phony money in Europe, but first mate Nick Shaw believes the captain was innocent of such plans. He sets out to clear his name. The real counterfeiter, gangster Thomas Nagle and his girlfriend Norma Harrison board and with their gang take over the ship, holding the crew hostage. Shaw pretends to go along with the gang, which is running guns and counterfeit currency to Lisbon. But Shaw has no intention of letting them succeed.