"When the Devil cannot reach us through the spirit, He creates a beautiful woman to reach us through the flesh." Hermann SudermannWhen they were young children in Germany, Leo von Harden [John Gilbert] and Ulrich von Eltz [Lars Hanson] rowed out to the Isle of Friendship where, in the presence of Ulrich's younger sister Hertha [Barbara Kent], they cut their wrists and vowed to be blood brothers forever. And so they have remained through school and military service, the one always looking out for the other. Even Pastor Voss [George Fawcett] admits that, although he christened them separately, he's never since seen them apart. All that is about to change.Leo and Ulrich are on military furlough and have returned home together where they are greeted at the train station by Leo's mother [ Eugenie Besserer] and Hertha, who is now almost 16 years old. As they are about to gather up their bags and depart from the station, Leo sees a beautiful woman debark from the train and walk to a waiting carriage. When she drops her bouquet of flowers, Leo hurries over to pick it up. Their eyes meet, and it is love at first sight.They meet again that very evening at the ball at Stoltenhof, which marks the opening of the social season. One look at her seated across the ballroom, and Leo leaves Hertha, who saved her first dance for him, standing alone on the dance floor. One dance later, and the lovers retire to the garden terrace. A shared cigarette later, and they are liplocked. Throughout Leo's furlough, they are inseparable. The day before Leo is to return to the military base to serve out his last five months of duty, his world collapses. While languishing in his lover's arms, her husband comes home. The love of Leo's life is Countess Felicitas von Rhaden [Greta Garbo], and Count Rhaden [ Marc McDermott] is not amused.Rhaden challenges Leo to a duel, first warning him that no scandal can come to the Rhaden name, so they stage the duel under the pretext of a dispute during a card game. Ulrich attempts to talk Leo out of the duel, but Leo is adamant. He and Rhaden begin their pacing, two shots are fired, and Rhaden is killed. Following Rhaden's death, the military court "advises" Leo to sign up for a five-year stint in Africa, which means being separated from Felicitas. Felicitas promises to wait but is worried about being alone for so long. Who better to console the grieving widow and see to her needs in Leo's absence than Leo's blood brother Ulrich. A last kiss stolen in a park where Leo thinks no one will see him and Felicitas together, and Leo is off for Africa. Unfortunately, someone does see them -- Pastor Voss.Three years pass. Leo gets a letter from Ulrich saying that he has been pardoned through the intervention of His Majesty and that Leo is free to return home. All the long way back from Africa to Germany, Leo can think only of seeing his beloved Felicitas again. He is met at the train station by Ulrich, Felicitas, and another surprise. Felicitas has become Ulrich's wife. Leo is devastated. Not even the happy reunion with his mother and with little Hertha, who is now 18 years old and living with Leo's mother since Ulrich's marriage, can take Felicitas off his mind.Although he refuses to promise Pastor Voss to never again see Felicitas, Leo stays away from her and avoids Ulrich, too, much to Ulrich's dismay. Eventually, after Felicitas and Leo have a heart-to-heart on the Isle of Friendship and Felicitas tells him how he is breaking Ulrich's heart, Leo resumes his friendship with Ulrich. Of course, this includes being around Felicitas, and Pastor Voss finds the three of them paling around together to be sinful. After Voss delivers a firey sermon, to the entire church but obviously directed at Leo and Felicitas, about David's seduction of Uriah's wife , Leo begins to avoid Ulrich and Felicitas again.One day, with Ulrich off in Munich, Felicitas pays Leo a visit at his home. She begs to talk with him, but he refuses to do so where his mother or Hertha might overhear, so they begin walking into town. It is winter, and the snow is freezing Felicitas' feet, which are clad only in high heels. Felicitas forces him to stop at a gardening cottage where a fire is blazing so that she can dry out her shoes. There is no one else in the cottage and, before long, they're in each others' arms, professing their love. Felicitas convinces Leo that the only thing left for them to do is to run away together, so they make plans to leave that very evening.Felicitas goes home to pack, but she is surprised when Ulrich comes home early from Munich. Not only that, but he brings her a present -- an elaborate diamond bracelet. She puts the bracelet on, takes the bracelet off, puts it on again, takes it off again, and finally puts it back on. She orders the maid to return her clothes to her closet and, when Leo arrives to pick her up, Felicitas tells him that she's not brave enough to leave everything that Ulrich has given her and that she's not going to run away with him after all. She intends to stay with Ulrich but wants to continue having Leo as her lover.Leo is both mortified and furious. In his anger, he grabs her by the throat and begins choking her. Suddenly, Ulrich enters the room. His eyes blazing, Ulrich asks what Leo is doing there. Felicitas throws herself at Ulrich's feet and tells him that Leo broke in and, when she refused to go away with him, tried to kill her. Leo upholds her story and tells Ulrich to shoot him where he stands. Although looking as though he'd love to do just that, Ulrich refuses and defers the duel until the next morning when they can meet on the Isle of Friendship.It being the dead of winter, it is not difficult the next morning for Leo and Ulrich to cross the frozen lake to the Isle. Warm and snug in her bed, Felicitas sit stone-faced as Hertha begs and pleads with her to stop the duel. When Hertha realizes that Felicitas has no intention of doing so, she falls on her knees and begins to pray for divine intervention. Felicitas goes ballistic, but Hertha keeps praying. Suddenly, Felicitas' face softens, she embraces Hertha, then throws on her coat and heads for the isle.On the Isle of Friendship, Leo and Ulrich have selected their guns. Pacing through the knee-deep snow, they turn on each other. Ulrich aims, but Leo refuses even to lift his gun arm until Ulrich reminds him that he intends to shoot to kill. Leo then raises his gun but points it haphazardly. Ulrich continues to aim but cannot shoot. Ulrich drops his gun and embraces his blood brother, telling him that all has become clear to him...the duel with Rhaden...Felicitas...and Leo. .Meanwhile, in parallel editing,unknown to either Leo or Ulrich, Felicitas has been hurrying across the ice to the isle when, suddenly, she steps in a patch of thin ice and falls into the frigid water; after their aborted duel their is a cut back to where she fell in and a few bubbles come up, and then nothing is left but her scarf floating on the surface.Alternate Ending: It is summer. Leo and Ulrich have remained friends since Felicitas' death and are in the garden helping Leo's mother wind yarn when Hertha prances by with her suitcases and boards a carriage. She announces that she is moving to Munich and never coming back. As the carriage starts down the road, Leo races after it, pulls Hertha from her seat, and begs her to stay. Hertha smiles demurely. [Original synopsis by bj_kuehl]