Late one night, former Navy lieutenant Chris Waring is roused from Gilhooey's flophouse by police and taken to Admiral Curtiss, his ex-commander. Curtiss tells Chris that he had recommended leniency when Chris was dismissed from the service for a drunken escapade, then asks for his help with an undercover operation. Curtiss explains that shipping magnate Arnold DeBrock has been selling his ships to the United States government, but the vessels mysteriously wind up in the hands of foreign powers. Hoping to employ Chris's well-known playboy tendencies, Curtiss asks him to get to DeBrock through his philandering wife Valerie. Chris declines, but when he sees a beautiful woman boarding a ship to Havana, the same one that Valerie is to sail on, he changes his mind and pursues her. After a vigorous flirtation with the woman, Chris takes her to his cabin, where he is surprised to find Joan Millard, Curtiss' secretary. In response to Joan's assertion that she is Chris's wife, the woman reveals that she is Valerie and leaves. Joan tells the stunned Chris that Curtiss sent her to help him, and the pair begin their investigation. Later, a castaway is brought aboard and Chris learns that he is Captain Jonathan Hunt, one of DeBrock's captains who was put adrift by his crew when he refused to follow DeBrock's orders to put into a foreign port and relinquish his ship. Captain Brigham and the ship's doctor drug Hunt in an attempt to force him to give the orders to them, but Hunt refuses. Chris rescues Hunt, and Brigham believes that a coffin he buries at sea contains Hunt's corpse. Meanwhile, Chris continues his flirtation with Valerie, which is reported to DeBrock by his right-hand man, Greb. Upon docking in Havana, Chris and Joan check into their hotel, while DeBrock castigates Brigham for killing Hunt. Following DeBrock's orders, Greb murders Brigham to prevent him from talking. DeBrock then tries to reunite with Valerie by telling her that he will retire from business soon and take her away to a secluded spot. Valerie, who does not love her husband, is distraught at the news and tells Chris that after an important meeting, DeBrock will be giving up his business. Soon after, Greb attempts to shoot Chris, for DeBrock has learned his true purpose and wants him out of the way. During the pursuit of Greb, Chris learns that Carlos, a handyman, is actually part of the Cuban military intelligence assigned to protect him and investigate DeBrock. With Carlos and Hunt standing by, Chris and Joan attend a farewell dinner given by DeBrock, during which DeBrock intends to signal Greb to kill Chris. DeBrock cannot give the signal, however, because he is shocked by the appearance of Hunt, whom he believes is a ghost come to haunt him. Hunt then interrupts DeBrock's meeting with his cohorts just as he is about to order his ships to sail to foreign ports. Carlos comes in and arrests all the participants, and Chris forces DeBrock to order his vessels to report to American ports. When Joan and Valerie rush in, DeBrock tries to get Chris's gun and falls out a window during the struggle. With the case solved, Chris and Joan prepare to sail back to America, and Joan is thrilled when Chris asks the captain to marry them.