Aside from a love for hoops, it would seem that Lucas and Nathan are two young men with little in common, but they are bound by the dark secret that they share the same father. Nathan is the star of the high school basketball team and local town hero, while Lucas is the only child of a single working mom. Now the two boys' lives collide when a twist of fate puts Lucas on Nathan's team and the half-brothers compete, not only for control of the court, but also for the heart of Peyton Sawyer, Nathan's beautiful, blonde girlfriend.
Lucas blows his first varsity game and decides to quit the team. The wedge between Nathan and Peyton continues to grow after Peyton tires of Nathan's jabs at Lucas. Meanwhile, Keith forces Karen to deal with her feelings for Dan after she refuses to step foot in the high school gym to support her son. Lucas learns of Peyton's artistic talent, even though she doesn't seem ready to inform the world about it.
Annoyed by Lucas's growing popularity, Nathan searches for his weak spot and finds it in Haley James, Lucas' best friend. After convincing the team to aggressively haze Lucas, Nathan seeks tutoring help from Haley and tries to befriend the girl. After all, nothing could hurt Lucas more than seeing his best friend help his worst rival. Meanwhile, Brooke develops feelings for Lucas, Karen must face some not-so-friendly acquaintances from the past, and Peyton becomes furious with Lucas when she discovers that he secretly submitted her drawings to a local newspaper.
Haley is apprehensive when Lucas decides to go with the team to an after-party at Nathan's beach house. When Lucas sees the wealth that was denied him, he finally confronts his mother about why she let Dan ignore them. Meanwhile, Nathan's mom turns to Karen for advice and Peyton and Nathan grow further apart.
Lucas asks Keith to play with him in the annual "Father and Son" basketball game, and realizes he got the better father figure after Dan publicly humiliates Nathan on the court. Meanwhile, Peyton turns down Nathan's attempts to make up. She is actually having a hard time dealing with the anniversary of her mother's death and finds a comforting ally in Whitey. Haley continues tutoring Nathan and their developing friendship bothers Lucas.
When Whitey throws Lucas and Nathan off the bus for misconduct, the two boys wind up stranded thirty miles from home. On the long walk home, they encounter a carload of punks who kidnap them at gunpoint. Injured during the game, Brooke needs Peyton to drive her home and Haley reluctantly accepts a ride with them. Meanwhile, Karen and Keith attend a business function, and tempers flare when Dan and Deb are seated at their table.
The night of Dan and Deb's annual basketball appreciation party stirs up old wounds and new feelings. As Karen makes a new friend, Keith faces off with Dan once again and Lucas finally makes his move on Peyton. Meanwhile, Haley and Nathan grow closer until Brooke spreads a vicious rumor that leaves Haley devastated.
Looking for some fun, Brooke and Peyton crash a college party, but things turn ugly when one of the guys in the dorm drugs Peyton. After Brooke calls Lucas for help, the two bond over caring for a sleeping Peyton, prompting Lucas to look at Brooke in a new light. Meanwhile, Haley gives Nathan another chance (thanks to Brooke) and the two go on their first date.
After fighting with his father and Haley, Nathan succumbs to the pressure he is feeling and takes amphetamines to help his game. However, he isn't prepared for the destruction the drugs do to both his body and his family. Meanwhile, Peyton goes to Lucas to rekindle their relationship, but when she arrives at his house, she catches him with Brooke.
Lucas is faced with an impossible decision: should he date Brooke or Peyton? Elsewhere, Whitey makes a controversial choice by canceling practice to help the team refocus. Meanwhile, Dan takes Nathan on a weekend outing in an attempt to reconcile with his wife and son, and Deb and Haley plan an open-mic night at Karen's Caf .
With Whitey's cancellation of basketball practice, Nathan takes advantage of his extra free time to see more of Haley. The couple spend an afternoon at his beach house, where the liquor flows. The Scotts see a therapist to try to fix their family problems, but the distance between Deb and Dan continues to grow. Meanwhile, Brooke grows jealous of Peyton's deepening bond with Lucas.
Emotions run high when Peyton discovers that her father is lost at sea and she and Lucas travel to Hilton Head Island to identify a body that has washed ashore. Overcome with emotion, Peyton gives in to pent-up feelings and kisses Lucas, while girlfriend Brooke waits at home. Meanwhile, an unexpected visit from Dan's parents leaves the Scott family in turmoil, as long buried secrets surface at a family dinner.
On their way to pick up Karen from the airport, Keith and Lucas' car collides with an oncoming vehicle and an unconscious Lucas is left fighting for his life. Having witnessed the accident, Dan races Lucas to the hospital and must acknowledge that Lucas is his son in order to save his life. Meanwhile, a guilt-ridden Peyton decides to tell Brooke about the kiss she and Lucas shared.
While holding a vigil at her coma-stricken son's bedside, Karen meets her Lucas' new girlfriend and learns that Deb and Dan are getting divorced. Most shocking of all, Karen is horrified to discover that Keith had been drinking before driving at the time of the accident. Meanwhile, Nathan tries to win Haley back after she dumps him.
After his near-death experience, Lucas decides he made the wrong choice between Brooke and Peyton, so he breaks things off with Brooke and secretly rekindles his romance with Peyton. However, the truth becomes obvious after he is rushed to the emergency room again and the girls come face to face in the hospital. Meanwhile, unable to pay his mortgage after paying for Lucas' hospital bill, Keith puts his garage up for sale.
Nathan must decide which parent to live with after the divorce, but Dan decides to force his hand by threatening to reveal Deb's darkest secrets in court unless Nathan chooses him. Meanwhile, Lucas meets a beautiful stranger who makes his head spin. Grammy Award-winner Sheryl Crow appears as herself and performs the song "The First Cut Is The Deepest" in Karen's Caf.
The gang hits the road to Charlotte where Brooke is determined to win first place at the annual cheerleading competition. But when one of her squad member falls ill, Peyton begs Haley to step into the cheerleader's shoes for a day. Meanwhile, after Whitey assigns Lucas and Nathan to the same room, tempers flare and Haley is caught in the middle.
Lucas, Nathan and Jake are auctioned off to the highest bidder in the annual "Boy Toy" charity auction and the night leads to surprising developments with old flames. Meanwhile, having missed out on the auction, Brooke ends up with Mouth and gives him the night of his life. Keith proposes to Karen, after Peyton's father lets her know he would love to date her. Astonishing news for Lucas: Brooke might be pregnant.
Lucas finds out that Brooke is with child and must make a decision regarding the pregnancy. Brooke gives Lucas the cold shoulder regarding the situation. Meanwhile, Haley considers giving her virginity to Nathan.
Nathan looks for an after school job to pay his rent and looks forward to the party that Haley is throwing for him. However, Haley panics when things get out of control. Meanwhile, When Brooke realizes that she isn't considered a close enough friend to rate an invite, she decides crash the party with her new friend, Nicki. The realization that Nicki is the random girl Lucas hooked up with leaves Peyton shocked and disappointed in her new boyfriend.
The pressure to perform intensifies for the Scott brothers when Dan becomes temporary coach of the basketball team. Nicki manages to steal Jenny under Peyton's watch and a terrified Jake blames Peyton for it. Meanwhile, Tree Hill relationships are in trouble as Karen and Keith's romance grows rocky, Dan gives Deb divorce papers, and Nathan and Haley hit the skids.
In the season finale, Lucas and Nathan bear the brunt of Dan's abuse as he coaches them into the playoffs, pushing both of them to their breaking points. Lucas is stunned when Haley's reconciliation with Nathan heightens the intensity of their relationship. Meanwhile, Whitey learns that his medical condition may be more serious than he first expected, and Dan learns a shocking secret about Deb and Keith.