A plan to devaluate U.S. currency was concealed on a valuable emerald by a U.S. spy, and the emerald was inadvertently obtained by Victor Tomar, an international arms dealer. Tomar is traveling by ship, as is Yorgi Petrosian, an enemy agent sent to recover the emerald. Rollin as a card shark gets together with Petrosian and they make a deal - Rollin will cheat Tomar and give Petrosian the gem and keep the winnings. Cinnamon tricks Tomar into getting to a game when Jim pretends to take her expensive bracelet. Tomar loses to Petrosian, but Rollin double-crosses Petrosian and gets the cash and the emerald. Petrosian tries to kill Rollin but Willy knocks him out and they fake that he's been lost overboard and found by a passing trawler. Petrosian wires a message to his aide, William, to kill Petrosian. Then they knock out Petrosian, put him in Rollin's cabin with a mask, and Williams kills Petrosian-as-Rollin and disposes of the body.
