Two years prior, Tim Thomas (Will Smith), reading a text message while driving, causes a car crash in which seven people died: six strangers and his fiancee, Sarah Jenson (Robinne Lee).
In a bid for redemption, Tim sets out to save the lives of seven good people. A year after the crash, having quit his job as an aeronautical engineer, Tim donates a lung lobe to his brother, Ben (Michael Ealy), an IRS employee. Six months later he donates part of his liver to a child services worker named Holly (Judyann Elder). After that, he begins searching for more candidates to receive donations. He finds George (Bill Smitrovich), a junior hockey coach, and donates a kidney to him, and donates bone marrow to a young boy named Nicholas (Quintin Kelley).
Two weeks before he dies, he contacts Holly and asks if she knows anyone who deserves help. She suggests Connie Tepos (Elpidia Carrillo), who lives with an abusive boyfriend. Tim moves out of his house and into a local motel, taking with him his pet box jellyfish. He later goes to Connie's house to speak with her about her problem, but she denies that anything is wrong, and asks him to leave. He sets down his business card, urging her to "think about it", as he is ushered out the door. One night, after being beaten, Connie contacts Tim and he gives her the keys and deed to his beach house, with the stipulation that she never tries to contact him, and never tells anyone how she came to own the house. She takes her two children and moves into their new home.
Having stolen his brother's credentials, and making himself known by his brother's name, Ben, he checks out candidates for his two final donations. The first is Ezra Turner (Woody Harrelson), a blind meat salesman who plays the piano. Tim calls Ezra Turner and harasses him at work to check if he is quick to anger. Ezra remains calm and Tim decides he is worthy.
He then contacts Emily Posa (Rosario Dawson), a self-employed greeting card printer who has a heart condition and a rare blood type. He spends time with her, weeding her garden and fixing her rare Heidelberg Windmill press. He begins to fall in love with her and decides that as her condition has worsened he needs to make his donation.
Tim's brother Ben tracks him down at Emily's house, demanding that Tim return Ben's IRS credentials. After an interlude with Emily, Tim leaves her sleeping and returns to the motel. He fills the bathtub with ice water to preserve his vital organs, climbs in, and commits suicide by pulling his box jellyfish into the water with him. His friend Dan (Barry Pepper) acts as executor to ensure that his organs are donated to Emily and Ezra. Ezra Turner receives his corneas and Emily receives his heart. Afterward, Emily meets Ezra at his concert at a park, and they begin to talk. Ezra cries, and they hold each other.