Twins Brandon and Brenda begin school at trendy West Beverly High after moving from Minnesota. Brandon joins the newspaper and meets Andrea Zuckerman, the intelligent and devoted editor. Brenda is befriended by snobbish Kelly, who picks her as a chemistry lab partner to avoid being paired with a fat girl. A rich but reclusive girl invites the entire school (except the freshmen) to a party at her house, complete with a live rock band. Freshmen David and Scott crash the party, and the drunken Steve asks David to drive him home. David accidentally damages the car, prompting Steve to begin a frantic search for the culprit. Brandon connects with the hostess, Marianne, and goes on a date with her. He insinuates that they slept together, prompting rumors to fly at school. Andrea is disappointed in him. Brandon clears the air about Marianne over the campus radio station. He follows Andrea home to explain himself, and discovers that she lives out of district. Brenda and her friends get fake IDs

Brandon meets Dylan McKay, a mysterious loner who stops some jocks from harassing Scott in tech class. Dylan takes Brandon surfing and introduces him to his friends, including a troubled young woman named Sarah.

Brenda goes on several shopping trips with Kelly and Tiffany, Kelly's best friend from junior high school. Brenda cannot afford the merchandise, and considers stealing because she is envious of her classmates' wardrobes.

Sheryl, Brandon's old girlfriend from Minneapolis, stays with the Walshes for the weekend. A concerned Cindy asks Jim to have a talk with Brandon. Before he gets around to it, Sheryl spends the night in Brandon's room. Sheryl seems obsessed with wealth and fame, and takes a liking to Dylan and his Porsche. Brandon believes that Dylan is hitting on Sheryl and punches him. Brandon is stunned to learn that he was not the first guy to sleep with Sheryl. Sheryl's mother calls Cindy and reveals that her daughter ran away following a fight with her stepfather. Brenda babysits for her handsome algebra teacher, with "help" from Kelly and Donna. She no longer finds him appealing after watching his wife push him around.

Jim encourages Brandon to try out for the basketball team. Steve, unaware that he is terrible, is bitter about being cut from the team. He tells Brandon that several of the players are ringers brought in from out of district to help the team win a championship.

Brandon is getting a C in American History because of the teacher's unreasonable grade curve, in which 80 percent of the students receive C's regardless of their marks. Steve scores an A on every test because he obtains copies of the exams beforehand. Feeling pressure from Jim about his grades, Brandon cheats on a quiz. Andrea is furious, particularly when her grades slip as a result. Brandon is faced with a moral dilemma when Steve offers him a copy of the midterm. Brenda tries to dye her hair blonde in the hopes of impressing Dylan, but winds up looking like a clown. Dylan flirts with Brenda and takes her to a stylist to repair the damage.

Brenda is mesmerized by Kelly's hip and glamorous mother Jackie, a former model. Kelly insists that her mother is not all that she appears to be. Jackie is a recovering addict, and begins hitting the bottle again after her boyfriend dumps her. Cindy is hurt when Brenda initially fails to ask her to be in a mother-daughter fashion show. They eventually agree to appear, and are joined by Andrea, who draws raves. Jackie attempts to emcee the show while high on cocaine. She becomes disoriented and disrupts the show with a rambling tirade. Kelly convinces her to check into rehab. Kelly gains new respect for David when he gives her the fashion show tape to save Jackie from embarrassment. Jim becomes addicted to his new keyboard.

The Walshes celebrate their seventeenth anniversary, but Cindy feels dissatisfied because Jim is neglecting her for his work. She has a chance meeting with old flame Glen, a talented artist. The two spend a lot of time together, and share a kiss after Glen's opening. Brandon and Brenda take part in a college study on twins, but are distracted by their parents' marital problems. David becomes the new campus DJ after Steve chokes in his tryout.

Brenda becomes a trainee for a teen crisis hotline, although Andrea questions her devotion. Brenda violates the rules by taking a call after hours. The caller is a date rape victim, who suffers the same fate on three consecutive nights. Brenda is desperate to learn the girl's identity and help her. Brandon believes that a masseuse has a romantic interest in him. He also dodges a freshman admirer, who similarly gives the cold shoulder to Scott.

Brenda and Dylan continue their flirtation, and she accidentally catches him in the shower. They go out alone when Brandon has to stay home sick. Dylan loses his cool after a confrontation with his father. Brenda consoles him, and they end up kissing. Jim objects to the relationship because Dylan's father is considered ruthless and crooked. Brenda is prepared to go all the way, and is crushed when Dylan stands her up. He later explains that he had to move because his father skipped the country to avoid an indictment. Steve tries to make a pass at the speaker for a sex education assembly. She reveals that she has AIDS. Her speech prompts Brenda to slow things down with Dylan.

Brenda goads Brandon into taking her to a party at Donna's house. He voices his objections to alcohol, but Steve spikes his drink. He decides to go along with it so that he won't appear ""uncool."" Kelly gets drunk and sleeps with Steve. Cindy catches Brenda with alcohol on her breath, but Brandon gets by unscathed. Jim and Cindy attend a weekend retreat, where they are forced to spend all their time with an overly friendly couple. Brenda convinces Brandon to throw a party, but they agree not to drink. Word of the party spreads, and it quickly gets out of hand. Brandon drinks heavily and kisses a stunned Andrea. Kelly dances with the lovestruck David to avoid Steve's advances. Brandon tries to drive to the store and smashes his car. He is arrested for drunk driving. Dylan takes him to an AA meeting and reveals that he is an alcoholic.