Imaginative, impetuous and wild Diana (Evan Rachel Wood) cannot wait for her adult life to begin. While awaiting the final days of high school in the lush springtime, Diana tests her limits with sex and drugs as her more conservative friend Maureen (Eva Amurri) watches with concern. Then the two teens are involved in a Columbine-like shooting incident at their school and are forced to make an impossible choice.
In a flashback we can see Diana’s adulthood. She leads an apparently normal life as an art history university professor. She has a child, Emma, and she’s married to the professor who once gave a speech in her school about the power of visualization, how one can shape one’s own future in this way. We learn, however, that she feels guilty about something that doesn’t let her sleep.
One day she gets a call from Emma’s school. The nuns who run the school complain about her behavior. Later, at an ice cream parlor, Diana asks Emma not to hide any more as she is always doing. “You hate me,” Emma replies to her mother's reproaches. They leave the parlor abruptly and as they’re about to get into the car Diana sees her husband, the professor, with another woman. She hesitates about confronting him and instead remains in the middle of the street where she is hit by a pickup truck. On her way to the hospital she imagines that blood is escaping from her body. However in fact she hasn’t been hurt by the accident. What is happening is that she is remembering the complications she had following an abortion in her high school days.
The day of the 15th anniversary of the shooting a memorial is held at the school. We see Diana drive in front of the school several times until she finally decides to stop and bring in some flowers. As she enters the school she’s asked whether she’s one of the survivors. She doesn’t answer and simply walks inside, first leaving flowers on some desks and then moving on to the rest rooms where one of the shootings took place.
At that moment she gets a call from Emma’s school. Her daughter is missing. Diana is told that a pink piece of clothing has been found in the woods. She drives there and walks through the woods, shouting out her daughter's name. Emma appears before Diana’s eyes for a moment but then vanishes almost as soon as she has appeared.
We’re taken back to the rest rooms in the school where Diana left the flowers. This is the place where she and Maureen were forced to decide which of them should survive. Maureen had offered herself first, but the shooter asks Diana why it shouldn't be her. She acquiesces and asks to be killed. She is then shot and dies. All that we’ve seen earlier in the movie is what Diana had dreamed her adult life would be like. Emma is the girl she never had, the girl that she aborted.