What a difference a few seconds can make!
Sliding Doors is a 1998 British-American film which alternates between two parallel universes.
In the very beginning, Helen gets fired from her PR job, so she leaves the office, drops an earring in the lift (and a man picks it up for her) and rushes for her train on the London Underground to go back to her flat. But as she runs down, her life is split off and we follow the two paths her life could take depending on whether or not she misses the train. Throughout the rest of the film we see what would have happened in each scenario
In the future that unfolds if Helen boards the train. she gets home in time to catch her boyfriend in bed with another woman. Therefore she walks out. goes to a bar and runs into James, who recognizes her because earlier he chatted her up on the train. Over the next few days, Helen changes her appearance to make a fresh start, and goes on meeting James. They fall in love and, eventually, Helen discovers that she is pregnant. Believing it is his child, she goes to see him at his office, where she learns that he is married. Upset, she disappears, but James finds her and explains that he is separated and planning a divorce. Helen is relieved but, while walking out into the road, she is hit by a van.
In the timeline in which Helen misses the train, , she hails a taxi but gets mugged when a man snatches her handbag. gets robbed, goes to hospital and eventually arrives home to find Gerry alone in the shower. So she doesn’t discover her boyfriend’s unfaithfulness, but little by little, she suspects him of infidelity. When she learns that she is pregnant, she has no time to inform him because she receives a phone call, apparently for a job interview. After she leaves and the man is contacted by his lover and invited to her flat, seemingly to break up. Thinking that Helen is at her interview, he goes there. While in the house he answers the doorbell and sees Helen standing at the door, shocked to meet him there. The other woman informs both of them that she is pregnant. Troubled, Helen runs off and falls down the staircase.
In both timelines, after her accident (hit by a car or falling down the stairs) Helen is taken to hospital, happens to end up in the very same emergency room in both timelines and loses her baby.
In the timeline where she originally boarded the train, she dies in the arms of James, her new-found love; in the timeline in which she missed it, she recovers and tells her unfaithful boyfriend to leave for good. Before waking, she sees flashes of the other Helen’s life.
In the final scene (only in the “missed train” universe), James leaves the hospital after visiting his mother, and Helen leaves after ending her relationship with her husband. They meet in the lift, and Helen drops an earring which is picked up by James, mirroring the start of the film, where the man picks it up on the elevator after Helen is fired from her job. Before the doors close, James tells Helen to cheer up, and they repeat some words they exchanged in the beginning of the film. The frame freezes as she and James stare at one another, surprised.