Hansard plays a Dublin busker (listed in the credits as Guy) who works in his father's Hoover repair shop to supplement his street musician earnings. Irglová plays a young Czech immigrant (listed in the credits as Girl) who sells flowers on the street. She approaches him during one of his late night street performances and, despite his annoyance at the interruption, she persists in talking to him about his songs, then gets him to agree to fix her vacuum cleaner the next day. She does brings her Hoover by and uses it as an excuse to get him to eat lunch with her, where she piques his interest by telling him that she's a musician too. He agrees to hear her play, so they visit a music store where she often plays piano. He teaches her one of his songs, which she picks up quite easily, and as they sing and play it together they kindle a musical connection and a romantic attraction. But when he propositions her at their end of the first day they spend together, she is insulted. They quickly patch things up as musical collaborators, and over the course of a week they excitedly write, rehearse and record songs, and spend time getting to know each other. The music continues to be performed in a real-world incidental music fashion, as the Guy plays to the Girl on the bus, or she rehearses her lyrics for his song to herself while walking down the street, and so on.
Their flirtation continues, but at the same time, he is thinking about and writing about his ex-girlfriend, who's moved to London. The Girl encourages him to move there, win his girlfriend back and pursue his musical career. It turns out that she has a baby and lives with her mother. The Guy decides that it is time to move to London, but he wants to make a high-quality demo of his songs to take with him, and he asks the Girl to record it with him. They secure a bank loan and reserve time at a studio. She reveals, much to his consternation, that she's married, though her husband is still in the Czech Republic. They recruit musicians to record the demo with them, rehearse, and record the songs successfully, staying up all night. He asks her to come with him to London, but isn't prepared for the reality of her mother coming along to help with the baby. Still, he is smitten, and asks her to come over and spend his last night in Dublin with him; she says that it would only result in "hanky-panky," which is a bad idea, yet she ultimately agrees to come over. But she stands him up, and the next day he can't find her to say goodbye before his flight. Before leaving for the airport, he makes arrangements to leave her a wonderful gift (a piano in the music store that she'd had her eye on, but not the money to buy it), then calls his ex-girlfriend, who is happy about his imminent arrival in London. The Girl's husband moves to Dublin and they reunite. Despite not ending up as a couple, the Girl and the Guy were deeply affected by their short time together.
