Mary Barrett is an aspiring opera singer who is taken under the wings of a famous operatic maestro, Guilio Monterverdi. After spending endless working hours together and arguing, their relationship develops into love. But, jealousy and misunderstandings prevent Mary and Guilio from acknowledging their true feelings.

Aircraft are being shot down by a large black plane with a big "X" painted on the wing. The chief suspects are invited for the weekend to an old dark mansion.

Against the backdrop of Vienna's hidebound caste system, aristocrat and army officer Nicki is attracted to peasant Mitzi, although he knows it cannot last. Acquiescing to familial pressure, he ultimately gives her up to marry the more socially acceptable – albeit crippled – heiress Cecelia. Mitzi, for her part, is heartbroken and must resign herself to marrying churlish butcher Schani Eberle.

Police detective Lanny resents the ongoing interference of the local FBI branch. Hoping to show up the feds, Lanny tackles a baffling espionage case. Things heat up when reporter sweetheart Ollie is framed for murder.

Kay Denham is off for a fling in Paris, leaving her suitor Berk behind. There, she meets two new suitors, Gene and George. Gene smooth-talks her into a junket to Switzerland, but George (with no illusions about his friend) appoints himself chaperone. Through a series of slapstick winter sports, Kay remains puzzled about George's disapproval of Gene...but there's a reason.

During World War I, Rin-Tin-Tin finds that he must rescue his master, a fighter pilot, from his wrecked aircraft. He also has to help him escape his rival, who has ordered him shot so he can have the girl they're competing for all to himself.

A radio correspondent tries to rescue a burlesque queen from her marriage to a Nazi official.

When the Great War breaks out, brothers Roy and Monte Rutledge, each attending Oxford University, enlist with the Royal Flying Corps.

A married singer, pianist/composer team are struggling to hit it big in New York. Finally, they audition before a Broadway producer, but the producer only wants the singer, leaving the husband without a job and feeling a failure.

A tugboat captain serves under his rival as a U-boat chaser in World War I.