On the day before commencement, Kelly becomes determined to oust Valerie from the Walsh house (and town) and pressures Brandon to do so. Meanwhile, Donna decides it's time to move up to a new level of romance with David after getting advice from her grandmother. Steve plans to pull the "best senior prank ever" with some help from his frat brother Muntz, as well as David.

Living together begins to take its toll on Kelly and Brandon's relationship. Donna asks David to move back in with her at the beachfront apartment, but with a stipulation that they sleep in separate rooms and that he doesn't tell her parents. Meanwhile, Steve has a couple of run-ins with Carly Reynolds - a young, overprotective, sarcastic, single mother with a six-year-old boy named Zack - who Steve wants to know more about.

With Kelly recovering in hospital from a drive-by shooting in an LAX parking lot, Brandon searches for the shooter and his partner who were responsible for the car theft that Kelly witnessed. Meanwhile, Donna lands another job at a prestigious fashion company and, after much hesitation, finally tells her mother of her living arrangements with David. Steve has yet another run in with Carly and tries to help her financially by landing her a job at the Peach Pit. After spending a torrid night with Valerie, Noah makes a quick exit and refuses to associate with her again.

When a sex shop opens, Steve & Brandon want to cover it for the Beverly Beat. Kelly is not happy with the idea. When they also invite David and Muntz to join them, David gets a little crazy and buys stuff that Valarie doesn't like.

With a few hours before Brandon and Kelly's wedding, they continue to feel uncertain about the path they are on. Jim and Cindy Walsh arrive in town from Hong Kong to help plan Brandon and Kelly's wedding. Meanwhile, Valerie finally decides to get an AIDS test after Johnny confesses to her that he happens to be HIV-positive, and she asks David to come along with her for emotional support. Steve becomes dateless for the wedding when Sarah decides to go back to her husband after witnessing her friend's messy break up. After the caterer, Jacob, saves Donna's life, Donna agrees to go on a pretend date with him to make his ex-girlfriend jealous. This makes Noah jealous.

Steve goes crazy on a Year 2000 "Y2K" millennium planning, ignoring or avoiding planning a holiday trip with Janet. Noah becomes openly hostile to Matt after he is hired to sue Noah's late father's oil company for environmental pollution in a class action suit. Meanwhile, Katie returns to David and wants to move forward with him, without sex. While babysitting her half-sister, Erin, in her mother's apartment, a hidden camera catches Kelly and Matt having sex in which, as a result of circumstances, ends up in Gina and Dylan's hands. Wayne, a fashion model, makes a play for Donna while Noah pressures her to keep her distance to the guy. Also, Dylan and Kelly deal with the fallout after their fling in Mexico is found out by Gina.

Kelly finally learns from Mel that Gina had blackmailed him over his infidelity. But when Kelly tells David, he refuses to believe her or anyone thanks to his renewed involvement with Gina and her skill of manipulation. At the same time, Kelly's mother, Jackie, asks Matt to represent her in suing David's father, while their daughter, Erin, shows obvious signs of depression over the breakup. Meanwhile, Dylan goes to bat for Andrew when he loses his job at the community center. But Dylan's victory over the center is bittersweet when word of Andrew's homosexuality spreads among the kids in which they no longer want Andrew around. Kelly also has to deal with Noah's presence in the beach front apartment which takes up space. Also, Steve and Janet's honeymoon is plagued by a series of mishaps and situations one of which includes a loud polka band playing in the room next to theirs.

Janet goes into premature labor near the end of the honeymoon and gives birth to a baby girl, while Steve maintains a vigil through the week as he worries about the safety of Janet and their newborn. Meanwhile, Dylan asks Kelly and Nat to volunteer in a feed-the-homeless Thanksgiving dinner at the community center. Kelly, seeking a way to boost Jackie's mood, asks her to help out with the dinner, while little Erin continues to mope about her parents' separation. Donna learns of a past indiscretion by her father with Gina's mother, which brings out revelations that could threaten to tear Donna's family apart. Also, David becomes uncertain about where Gina stands with him over her breakup with Dylan.

David and Donna announce their engagement in which all of their friends rush to give them the perfect wedding with Donna's mother, Felice, and Kelly's mother, Jackie, taking over the arrangements and Nat catering for the ceremony and agreeing to escort Donna down the church aisle. Meanwhile, Steve asks Janet to help him form their own publishing company so they both can have time for baby Maddie. Noah returns to Ellen and tells her that he has decided to give their relationship a second chance. At Donna's pre-wedding party, Kelly, Janet, Felice and Jackie are in attendance as well as friends from their past who include West Beverly High principal Mrs. Yvonne Teasley, as well as Andrea Zuckerman and even Valerie Malone. At David's bachelor party, Steve, Noah, Dylan, Nat, and David's father Mel attend the gathering as well as Steve's stepbrother Ryan and former KEG fraternity brother Munz, except for Brandon Walsh who sends his regards to everyone via videotape. The day of the wedding goes without a hitch and at the end, Matt shows up briefly to tell Kelly that he has decided to move back to New York, and she goes back to try to renew her relationship with Dylan.