Marie Galante, a pretty French deliverer of telegrams, is inadvertently abducted by a drunken sea captain bound for Central America. Escaping in Mexico, Marie travels down the coast trying to find a way back home to France. In the Panama Canal Zone, she finds work as a singer and piques the interest of several men: Tenoki, a Japanese merchant, Brogard, his German competitor, Ratcliff, a British diplomatic agent, and Dr. Crawbett, ostensibly a researcher into tropical diseases. In fact, one or more of these men is involved in espionage and a plot to sink the U.S. fleet as it passes through the canal. Naive Marie cannot believe anything nefarious is afoot, but the handsome Dr. Crawbett convinces her to help him uncover the saboteur. But Marie is not sure she can trust even Crawbett.