Continuing where last season left off, Nathan, Rachel and Cooper's lives hang in the balance after the accident. In the aftermath, Nathan is haled as a hero, but he begins to doubt that he was the one responsible for the life-saving actions. Haley is deeply affected by the accident and Nathan's near-death experience, especially when Nathan begins to shut her out. Meanwhile, Lucas confronts Brooke about the pregnancy test and Dan confronts Deb after finding that someone had written "murderer" on his wall.

Nathan, Cooper, and Rachel continue to deal with the aftermath of the car accident, each of them struggling with their emotions in their own way. Meanwhile, Brooke celebrates her 18th birthday alone due to her issues with both Lucas and Peyton. Elsewhere, Lucas and Karen come to terms with Karen's pregnancy without Keith, and Deb's addiction has explosive results at the cafe.

As Lucas and Brooke butt-heads at a party, Haley begins to realize that Rachel is trying to get closer to Nathan. Meanwhile, Peyton reaches out to her half-brother, Derek; Skills makes his debut with the Raven's basketball team; and Rachel reveals that she knows who's pregnant.

While rumors that Brooke is pregnant spread around Tree Hill High as well as the town, Peyton is able to get hip-hop artist Lupe Fiasco to perform at TRIC. Nathan, still recovering from the car accident, buys a motorcycle despite Haley urging him not to. Meanwhile, Lucas fights with Derek; Deb double-crosses Karen; and Rachel poses for Maxim magazine.

Derek's real intentions are exposed and when Lucas tries to save her from him, Derek becomes violent and attacks Peyton. As rumors continue to fly about Brooke being pregnant, Brooke sets everyone straight as to who is really pregnant. Meanwhile, Nathan receives a scholarship offer from Duke, but also receives life-changing news that forces him to rethink his scholarship offer. Elsewhere, Deb tries to break her prescription drug habit in order to go to Nathan's press conference sober.

Nathan and Haley's financial problems continue to mount, leading Nathan to turn to his father for help. Lucas decides to rejoin the Ravens, despite his heart condition. Meanwhile, Peyton, feeling alone, finds comfort in an unlikely source; Brooke is horrified to discover who the man she's been dating really is; Mouth is surprised by an unexpected offer; and Daunte, an old friend of Dan's, arrives in Tree Hill.

As Tree Hill is buzzing about Rachel on the cover of Maxim magazine, Brooke is put to the test as she deals with a model at the T.A.R.T. fashion as well as Nick. Lucas finds out about Nathan's dealings with Daunte, forcing Lucas to have to choose between Nathan or his love of the game. Meanwhile, Haley gets a taste of things to come when she agrees to babysit, but soon finds herself in over her head; and Peyton, with the help of Derek, forces herself to conquer one of her deepest fears.

Derek finally convinces Peyton to follow her heart and be with Lucas just as Brooke decides that she wants to get back together with him. Both Nathan and Rachel turn to unlikely people for help -- Nathan to his father for help with Daunte's latest demand and Rachel to Haley for tutoring after she receives an F. Meanwhile, at the annual Ravens sports banquet Nathan is named the team's MVP of the year.

As the state championship game approaches, Whitey prepares to coach the final game of his career while the team deals with the pressure of the once-in-a-lifetime game. Peyton finally admits to Lucas that she loves him, but Lucas is unable to repond right away. Meanwhile, Karen dishes out some tough love to Deb in order to help her deal with her addition; Haley learns the sex of her and Nathan's baby; Dan strikes a deal with Daunte; and Nathan and Lucas clash over the team and their own personal goals. However, everyone's emotions following the game are overshadowed when both Haley and Lucas are rushed to the hospital following a devistating accident.

After the accident, Lucas receives a shocking visitor -- his supposedly dead Uncle Keith. Keith guides Lucas through what life would have been like had Lucas not been the good guy he had been and pressures Lucas to remember what really happened the day Keith was murdered. Both Haley's life and the life of her child are threatened after experiencing serious pregnancy complications. Meanwhile, as Haley lies in a coma Nathan tries to deal with the guilt of his deal with Daunte; Dan tries to make things right concerning Keith's murder; and Peyton and Brooke work on becoming friends again.

Lucas, having recovered from his heart attack, returns to school with high-hopes of restarting his new relationship with Peyton. Haley learns that Nathan involvement with Daunte caused the accident, leading Haley to be very angry at him. Meanwhile, Brooke and Rachel team up to steal the answers of the next calculus exam from the tutor center; Deb plans to break out of rehab; and Dan accepts his fate when murder charges are brought upon him.

With senior prom nearing, Haley becomes increasingly frustrated with her slow recovery and with Nathan, leading Skills and Mouth to team up to help Nathan earn money -- by having him dance at a local strip club. Meanwhile, Brooke and Rachel's new friendship slips into their relationship of the past as Brooke betrays Rachel in order to get closer to a guy. Elsewhere, Lucas and Peyton continue to enjoy their new relationship and resolve to be happy while Deb makes a potentially life-ending decision.

Students of Tree Hill High are paired up for a class assignment that leads to everyone revealing their deepest hopes, secrets, and fears. Skills, worried about getting into college, turns to Haley for support, and Haley, in turn, leans on Skills for support when she worries about how having a family will change her life. Chase learns that Brooke cheated on her calculus exam, and spends the class period wondering what else Brooke has lied to him about. Lucas spends the class with Glenda and realizes that they have more in common than meets the eye. Meanwhile, Nathan reveals to Peyton that his mother tried to kill herself; Mouth's assignment turns romantic in nature; and Haley feels the baby kick for the first time.

Haley finds out about the stolen calculus test and confronts Brooke about it. As Peyton and Brooke continue to mend their relationship, Lucas and Peyton consider taking theirs to the next level. Meanwhile, with Deb away, Nathan throws a party for the senior class at his mother's house during which a sex tape from his past is exposed.

During Prom day, the effects of Nathan's pre-Prom party continue to ripple through Tree Hill. After seeing the sex tape that surfaced during the party, Haley confronts Nathan and demands a list of his past sexual relationships. Rachel is expelled from school after taking the blame over the stolen calculus exam for Brooke. Peyton admits to Lucas that she wants to skip Prom altogether, but Lucas sets out to change her mind and won't take no for an answer. Meanwhile, Mouth and Brooke each deal with dating a Clean Teen on Prom night.

Prom proves to be an unforgettable night for everyone when Lucas realizes who was in the hallway when Keith was killed. Meanwhile, Peyton's decision to skip Prom leads to a dangerous situation, but also leads to a reconciliation with Brooke. Elsewhere, Nathan and Haley attempt to be romantic teenagers during Prom, but find it hard to do; Dan tries to win over Karen, but as he does so the witness to Keith's murder closes in on Dan.

The gang head to Texas on a rescue mission to save Mouth from his ill-conceived road trip with Rachel. In Texas, the teens get another shot at the Prom and Lucas and Peyton decide to take their relationship to the next level. Meanwhile, Brooke confesses to Haley that she lied about stealing the calculus exam and Nathan once again has to face his past mistakes surrounding his dealings with Daunte.

The future with Duke that Nathan thought he had lined up is at risk when his past mistakes come back to haunt both him and Haley. Lucas hears a shocking confession after meeting the mysterious witness to Keith's death. Meanwhile, Brooke tries to make things right with her friendship with Peyton after having a run-in with Chase.

Nathan and Haley are able to grow closer as a couple despite the looming basketball scandal. Brooke contemplates her relationship with Chase after she senses a spark between them. Meanwhile, Peyton is given an offer that would force her to leave Tree Hill; Mouth and Gigi reconnect; and Lucas reveals to Karen who killed Keith, which sets off an explosive chain of events.

Graduation day arrives for the Tree Hill High seniors, bringing the realization of dreams for some, while the dreams of others are brought to an end. As Nathan deals with his future without basketball, Haley gets her valedictorian speech ready and she worries about being a mother in the matter of weeks. Meanwhile, Brooke makes a confession that may damage the future she thought she had and Lucas confronts his father when his mother's life is threatened.

In the fourth-season closer, Rachel returns to town to throw a graduation party for the Tree Hill High senior class. There, the teens say goodbye to each other as they each embark on their post-high school plans. Nathan and Haley adjust to life as parents while Lucas and Peyton prepare to part for the summer. Meanwhile, while recovering in the hospital, Karen has a dream about Keith and their daughter; Dan's grief and confession lead him to consider deadly action; and Karen confronts Dan about Keith's murder.