Cindy and Jim throw a party for their 20th wedding anniversary. As Stuart and Brenda's affair grows, he proposes marriage and she willingly accepts. Meanwhile, Brandon falls for an anthropologist grad student named Lucinda Nicholson. A paranoid Dylan buys a gun from a street dealer and almost shoots Brandon. Andrea tells Kelly that she has doubts about her affair with Dan after he tells her about his non-belief in marriage; then Andrea meets Jesse Vasquez, a charming Latino barman, at the party. Mel asks David to look after baby Erin while he heads off to Mexico with his girlfriend.

Brenda is bothered when Stuart tells her that his parents want her to sign a prenuptial agreement; Jim also finds out about Stuart's prenuptial papers and asks Dylan to look into Stuart's background. Meanwhile, David and Kelly grow more hostile to each other when they are caught in the middle of Mel and Jackie's custody battle for Erin. On his first dinner date with Lucinda, Brandon discovers that she is married... to his sociology professor. Guilt plagues Steve he does a favor for Sears and his frat buddies to bed blind date Laura Kingman, a professional college dancer.

When their wedding plans become too much of a hassle, Stuart convinces Brenda that they should elope to Las Vegas. After Brandon finds out, he gets the rest of the gang to drop what they are doing and they all fly out to Vegas to try to discourage Brenda and Stuart from their marital plans. Meanwhile, Laura wants to see more of Steve, who tries to keep things between them under wraps. On other personal fronts, Brandon continues to try to keep Lucinda distant who continues to flirt with him every chance she gets. Donna continues to try to resolve the continuing feud between David and Kelly.

After Steve breaks up with Laura, she tells Kelly and others that he date-raped her the night they were together to get back at him. Meanwhile, Kelly learns Sears true sexist colors and rejects him, but he too doesn't take it so kindly. Dylan tutors Brenda in poetry which brings them to a disagreement. Also, Brandon's relationship (or lack of it) with Lucinda takes a dangerous turn when D'Shawn finds out and threatens Brandon to take his history mid-term for him or he will tell Professor Randall of his suspicions. When Lucinda insists to Brandon that he should take D'Shawn's tests, Brandon reacts stressed and hits the road.

Strange dreams contemplate Donna to fulfill David's dream to sleep with her on their second anniversary together, until her parents show up for a surprise visit. Meanwhile, Brandon returns from San Francisco where he learns about the Steve's botch break-in, who finds himself left in cold after Mike Ryan and the rest of the frat members reject him. Only John Sears remains sympathetic to Steve and tries to help. But when Brandon learns and relays to Steve that the campus police were anonymously tipped off to Steve's break-in, Steve realizes that Sears had set him up. In the meantime, Brandon plays hardball with the corrupt Professor Randall to drop the break-in charges against Steve by threatening to go public about him rigging test scores for D'Shawn and other basketball stars to they can play basketball for the university. Elsewhere, Andrea falls deeply in love with Jesse. Also, John Sears continued wooing of Kelly only pushes her back to Dylan.

With Nat still in the hospital awaiting heart surgery, Brandon temporarily takes over running the Peach Pit, while Dylan rescues the place after he buys out Joey's share, making Dylan the co-owner. Meanwhile, David's drug problem returns, resulting in Kelly and Donna moving out and David losing his radio DJ job when Howard the station manager sees that he's completely out of control and fires him. Jesse objects to Andrea's decision to get an abortion. Brandon learns of Lucinda's divorce from Professor Randall and wants a relationship with her.

Donna tries to make up with David, whose increased drug use turns her away. David also steals $150 from his father to buy more amphetamines for himself. When his drug dealer is arrested later, he finds himself in possession of a huge stash of narcotics and calls on Dylan for help. Meanwhile, Jesse and Andrea meet with her grandmother to get her blessings before their wedding and reception at the Peach Pit. A dangerous affair begins between Brandon and Lucinda, who shows her true colors when she starts teaching her anthropology class of human sexuality and preaches the need for multiple partners, seeing sex as her personal weapon. Brenda gets a surprise visit from a long-absent Stuart on Valentine's Day.

Brandon uses Kelly as his date at a university social event to shield his affair with Lucinda from Josh Richland, a snooping student reporter from the Condor determined to dig up any dirt on Brandon. Meanwhile, Brenda and Stewart travel to Palm Springs where they find big complications from a small mistake Brenda makes which leaves them stranded in the desert, where Stuart fumes over and it resulting in her finally breaking off their engagement for good. David rents a piano as a new hobby while Kelly moves back in with him and Donna. Also, Andrea lets Steve use her dorm room after he can't stand living at the KEG house.

Lucinda temporally loses interest in Brandon when she flirts with Dylan to ask him to finance her documentary film. Meanwhile, Kelly and Brandon spend the weekend together at a task force retreat where they meet the university Chancellor, Milton Arnold, Dean Trimble and the Chancellor's teenage daughter Clare, where Brandon and Kelly become more attracted to each other and brush off Josh who's still hounding them. Brenda and Donna befriend a stray dog that escapes from the university's lab, whom they name Rocky. Also, Andrea discovers that Steve is allowing Muntz and his frat buddies to use her dorm room for nooners. Andrea protests, but changes her mind when Steve begins to date her dorm resident advisor, Kathy Fisher.

Brenda and Donna attend an animal rights rally, and are crestfallen when the university refuses to suspend animal testing. After Rocky dies of cancer, Brenda becomes involved with a small group of radicals. She serves as lookout when the group breaks into the university research building and tries in vain to save Andrea's lab (which does not harm animals in its testing). Brenda is arrested. Kelly and Brandon are furious when Dylan refuses to fund Lucinda's film. He finally tells Kelly that Lucinda came on to him. Brandon breaks up with Lucinda and Kelly confesses her kiss with Brandon. Dylan races over to the Walsh house to fight Brandon, but the tension is defused when he accidentally punches Steve.

Brenda calls Dylan from jail in the hopes of keeping her arrest a secret, but he is forced to tell her parents. Brenda's friends avoid her out of fear of being accessories after the fact and Kelly acts especially bitchy because she is tired of Dylan coming to Brenda's rescue. Brenda faces felony charges, as her crime was a federal offense. An FBI agent who had gone undercover with the activists offers her immunity in exchange for her testimony. Kelly apologizes for shunning Brenda. Andrea gives Donna a healthy puppy (Rocky II) to take her mind off Rocky's death. Steve and his overbearing father, Rush, take on a baseball star and his dad in a father/son golf tournament. Steve catches his father cheating and forces him to complete the game honestly. Lucinda receives a grant for her movie and leaves the university. Josh threatens to expose Brandon's affair with Lucinda unless he endorses his campaign for student president. Brandon calls his bluff and Josh eventually has second thoughts.

In the two-part season finale, Brandon goes to Washington D.C. as a part of the college task force to meet the president. Kelly follows Brandon to Washington to get him out of a jam when Clare and Lucinda arrive at the hotel to pursue him. At the CU Mardi Gras, David impresses pop star Kenneth "Babyface" Edmunds, and his recording manager Ariel with his keyboard music and Donna catches David in a very compromising position with Ariel. Steve runs into Celeste who's now with John Sears. Kevin and Suzanne get married in a semi-formal ceremony where he persuades Dylan to cut out any outside investment in their business offer. Jim becomes angry at Dylan for making such a rash move and Dylan fires Jim as his financial holder. Dylan then goes to a bank and gives Kevin full power-of-attorney control over his money, unaware that Kevin and Suzanne have had a hidden agenda for Dylan's inheritance all this time. After her major success in the CU play, Brenda gets a scholarship offer to study acting in London and she pays a visit to Dylan's place before leaving. Also, Andrea and Jesse experience the joys and fears of parenthood after their daughter is born.