Prince Rudolph (Boyer), continually rebelling against his father, Emperor Franz Joseph (Jean Dax), is forced into an arranged marriage designed to "keep him under control." All this fails when Rudolph meets the beautiful Marie (Danielle Darrieux). The two fall hopelessly in love and try in vain to keep their illicit affair secret from the prying eyes of the Emperor's spies.

One of Rudolph's enemies arranges for Marie to be taken away to Trieste for a "rest cure." Rudolph sinks into a drunken depression, snapping out of it only when Marie returns. They attempt to legitimize their love through marriage, but the Catholic hierarchy will not approve of Rudolph's divorcing his wife.

Desperate, the lovers flee to Rudolph's hunting lodge in Mayerling. Here they spend an exquisite last night together, then formulate a death pact. The following day, Marie and Rudolph are found lying side by side - united in death.
This film firmly established Boyer in the international movie-going public's mind as a romantic star of top quality.