The sarcastic Jonathan Breech (Cillian Murphy) is nineteen when his father dies from a destroyed liver due to too much drinking. After a night with a gram of cocaine, another man's girlfriend and already stolen convertible, he goes to his older brother Mikey's (Paul Hickey) house at five in the morning to get his father's ashes. With the urn in the back seat he then goes on a suicidal drive.
After waking up in a hospital he is given a choice: prison for the stolen car or a mental institution. He chooses the latter. His room there is small and very near barren. Wednesdays are visiting days, when his brother can come. The recreation room has a TV, cards and velcro-tipped throwing darts. Since he is an inpatient he is forced to only wear pajamas as per the health board rules.
He has three group therapy sessions a week with Dr. Figure (Stephen Rea). There, he meets Rachel (Tricia Vessey), Toby (Jonathan Jackson), Nick (Tomas O'Suilleabhain) and Leslie (Marcella Plunkett). He crassly voices romantic interest in Rachel but leaves the first session extremely early. Rachel follows him to slap him for treating her patronisingly. A brief game of play boxing starts, but stops when she accidentally hits his mouth hard and draws blood. Jonathan goes to the restroom to take care of his bloody lip, and Rachel follows him and shows an unsettling like of blood; smearing it on to her throat and chest. Jonathan is unsettled, but intrigued. He then befriends Toby, who seems to also have a crush on Rachel. One-on-one therapy sessions with Dr. Figure are sarcastic but do ask patients to take a pledge not to kill themselves before New Year's Eve.
His friendship with Toby starts to gel when they sneak out to a pub together at night. After retuning to his room, Jonathan is surprised to discover Rachel there waiting for him. Rachel invites him to fool around a little. While he is lying on top of her, Rachel pulls out a razor hidden in a cigarette box and cuts her arm, which seems to intensify her sexual excitement. When the blood drips onto Jonathan's neck, he puts a stop to things.
In the following days, Jonathan has therapy sessions with Dr. Figure, and continues to flirt with Rachel, showing a more sincere interest in her. One night out with Toby, after his hot-wired a car Jonathan learns that Toby caused the death of his brother in a car accident. On bowling night, Jonathan gets into conflict that nearly turns seriously violent, and Dr. Figure helps him see that he was reckless with his well-being but that perhaps he is glad to have made it through alive.
The romantic triangle comes into sharper focus as Toby reads a new poem he wrote to Rachel and flirts timidly. Later Jonathan and Rachel chat in her room and he learns of Rachel's mother's death, and a bond between them deepens.
The friends sneak out of the hospital to host a big New Year's Eve party at Rachel's father's house. Toby watches Jonathan and Rachel's energy as they dance together, and realizes that he doesn't have a chance with Rachel. Soon Jonathan and Rachel are seen going upstairs. In another part of the house Toby is opening up the garage. Jonathan tries to kiss Rachel but she won't kiss back. As the count down to the New Year begins Rachel starts to kiss back and Toby gets ready in the car to be done with his pledge. At the stroke of midnight Toby drives off a cliff, killing himself.
The next day, Rachel's father pulls her out of the hospital, and Jonathan is miserable and worried about her. In a therapy session he asks Dr. Figure what will happen to Rachel. Dr. Figure responds that Jonathan needs to decide to value his own life. When Jonathan steals a bike to get out of the hospital, Dr. Figure tells the guard to allow him to leave. Jonathan goes to Rachel's dad's house, then to the cliffs. He finds her there, looking over the edge. Jonathan tells Rachel that he loves her that he thinks they could still be together in a year. She walks away from the cliff's edge and they walk away together.