At Armistice time, three members of the A. E. F. become separated from their regiment attempting to retrieve some souvenirs. Looking for their company, they cycle into a Rhenish village and are accepted by the burgomaster as the new overlords. Jack Benson takes an interest in Elsa von Bergen, a wealthy aristocrat; and another personable girl becomes enamored of hard-boiled Lefty Mooney. With his friends, Jack invades Elsa's castle with the intention of "rescuing" her from some danger. She arranges a welcome with mysterious doors, traps, and other surprises, culminating in a battle with a ghost in ancestral armor. The trio are arrested, but through Elsa's influence they are released and the couples are happily married.
—AFI