Mary Justin arrives in Switzerland in 1948 to meet her husband. By chance, staying in the hotel room next to theirs is her former love, Steven Stratton. She and Steven meet and spend an innocent day together. Her husband, Howard, returns before he is expected. Having witnessed their parting, Howard angrily confronts Mary with his intention of divorcing her.

Through a flashback and then a flashback within a flashback, it is learned that Mary and Steven were lovers before her marraige. Frightened and wanting a lot out of life, Mary gives up the young biology professor she really loves for a wealthy banker and the security he offers. Five years later, Mary and Steven meet again at the Chelsea Arts Ball, and though she is already married to Howard Justin, a millionaire British banking lord, Mary falls in love with Steven once again. Thus once again, she is torn between love and the security which Howard's wealth offers. She decides to remain with her husband. Howard, in turn, forgives her with the understanding that she and Steven do not meet again, yet he remains frigid towards her.

During their final meeting in the train station, while they sit waiting for Alee's train, Myrtle Baggot, a talkative friend of Laura's ' joins them and is soon chattering away, totally oblivious to the couple's inner misery. As they realize that they have been robbed of the chance for a final goodbye, Alec's train arrives. With Myrtle still chattering away, Alec departs with a last look at Laura. As the train is heard pulling away, Laura suddenly dashes out onto the platform. The lights of the passing train flash across her face as she conquers her impulse to commit suicide; she returns home to her family.

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Synopsis written by Louis Castelli, Ph.D from his book, David Lean: References and Resources.