During World War I, John Stevens invents an anti-submarine device, but the plans are stolen by two German spies, the Baron von Wiederholtz and Madame Elsa, who flee to a New York hotel. Stevens' daughter Alice pursues the spies hoping to retrieve the plans. Also lodging at the hotel are Howard Skeele and Margaret Worth, childhood friends whose parents are forcing them to marry with threats of disinheritance. In attempting to escape, Howard finds himself in the baron's suite just in time to spy the German in the act of hiding the plans. Howard directs Alice to the plans, and then, because he must be wed before six o'clock that evening or lose his inheritance, he proposes to her. They marry with Margaret's blessing, the spies are arrested, and Alice returns home with the plans and a husband.