"One Day" is a film based on the David Nicholls best-seller about Emma Morley (Anne Hathaway) and Dexter Mayhew (Jim Sturgess) who meet after graduation on July 15th, 1988. They spend the night together but agree to simply be friends.
The next year, Emma is working as a waitress in a Mexican restaurant in London and Dexter is traveling the world, drinking and promiscuously going through several girlfriends. Eventually Dexter becomes a wealthy and highly successful television presenter on a raucous late-night show. Although meeting once in a while throughout the years, Emma meets Ian -- a comedian she doesn't find too funny. But the two start dating anyway and she becomes a school teacher.
Meanwhile, Dexter's once-glamorous mother (now diagnosed with cancer) is evidently unimpressed with the nature of his TV show. His father is also disappointed with him and bans him from the family house. The whole time, Emma is growing steadily more irritated with Ian, so she and Dexter organize a meeting over dinner.
Unfortunately, things get out of hand because Dexter gets drunk, insults Emma, gets up from the table, flirts with a blonde down the hall, and generally ignores her most of the time during this otherwise posh date. This results in the two making a public scene in front of the fashionable restaurant patrons and Emma storms off, suggesting that they break off their friendship entirely.
A few years later, Emma's former roommate gets married and both she and Dexter are invited to the wedding. There she discovers that Dexter now has a new fiancee, Sylvie, and is on the way to becoming a father. She tries to hide the fact that she is upset and they share a very brief "old-friendship kiss".
The next year, while Sylvie is out of the house under other pretenses, Dexter is trying to calm his new (wailing) daughter, Jasmine. Unbeknownst to him, Sylvie is actually having an affair with an old friend of his. They divorce.
Meanwhile, Emma and Ian (the comedian) split up and she becomes a published author. Emma and Dexter both move to Paris. Dexter hopes that they will get together again but Emma now has a new French boyfriend who plays piano in a jazz band. Smitten and taken aback by this knowledge, Dexter begins to leave. But Emma, having second thoughts, chases after him and catches up, resulting in their sharing a passionate kiss.
By the next year, they are now engaged, with Dexter running his own cafe which proves to be very lucrative. They start trying to have their own baby but are unsuccessful. Emma becomes irritated with this and Dexter promises that when she returns from work, they will go out for dinner. Unfortunately, that afternoon, while riding her bike out of a blind alley, Emma is violently hit by a truck and dies.
The next scene shows Dexter, in bed, red-eyed from apparent long hours of weeping. The film then flashes back to 1988, where, after they had been talking in bed for a while, they had gone for a walk on a hill. The story then goes back to the present day, in 2011, where Dexter visits the hill again; this time with his daughter who has now grown substantially. He reminisces about the day when he and Emma first met, and where they had exchanged phone numbers.
As they walk away from each other, Emma says she knows they will meet again. The film ends with her saying "Goodbye, Dex."
