The series revolves around the Wilson family, along with other rich teenage students at the fictional West Beverly Hills High, where Annie Wilson (Shenae Grimes) and Dixon Wilson (Tristan Wilds) begin attendance. Their father, Harry Wilson (Rob Estes), returns from Kansas to his childhood home of Beverly Hills with his family to care for his mother, former television star Tabitha Wilson (Jessica Walter), who has a drinking problem. Annie and Dixon struggle to adjust to their new lives while making new friends and adhering to their parents' wishes. 90210 features cast members from the original series; featured guests include Jennie Garth, Shannen Doherty, Tori Spelling, Ann Gillespie, and Joe E. Tata. However, after the conclusion of the second season none of these guests will be featured again.
Much like the original show, 90210 follows the move of a family (parents Debbie and Harry Wilson, their daughter Annie and adopted son Dixon). Harry is actually from Beverly Hills and comes back both to look after his mother Tabitha and to work as the principal at West Beverly Hills High School. All of them struggle to adjust to their new lives: Annie has a hard time balancing romances (starting with rich kid Ty) and friendships as well as popularity and identity; Dixon has issues with his adoption and African-American heritage; Harry and Debbie struggle with the revelation that Harry has a son with Tracy Clark, his former high school sweetheart.
Tracy Clark has a daughter of her own, Naomi Clark, who dates jock Ethan Ward, brief rival of Dixon, with whom she soon breaks up and who gets back with Annie with whom he had a fling years prior. Both girls alternate between enemies in a love triangle and almost sisters due to their parents' child. Their respective mothers find in a love triangle of their own after Tracy's marriage to Charles Clark implodes (which Naomi takes quite badly) and she appears to want Harry back. Naomi's fight with Annie forces her out of the crowd after she uses Annie's ex-boyfriend Jason as a weapon to get back at her for hiding her relationship with Ethan. She becomes friends with older girls and starts flirting with Ozzie, a rather alternative student and later becomes attracted to a bartender named Liam whom she soon finds out is actually underage and becomes a student at West Beverly High. Meanwhile Ethan and Annie's relationship hit the rocks as he begins to rethink his life after a car accident and gets more or less attracted to Rhonda, the girl he hit. Soon Naomi and Liam begin a fling, and once she becomes friends with Annie again, he begins to pursue the both of them.
Naomi's best friend, fallen starlet Adrianna Tate-Duncan battles a drug addiction. This gets her into trouble when Harry decides to clean the school, thanks to the help of a cop, Kimberly McIntyre, under cover as a student. Kimberly begins a relationship with teacher/lacrosse coach Ryan Matthews, which gets him into trouble with the school. Guilt-ridden, Kimberly does her best to solve the case, giving Ryan his job back, although he takes a leave of absence to rethink his life, and Adrianna lands in rehab, after almost getting Naomi in legal troubles as she took the blame for the drugs. There she begins a relationship with Navid Shirazi, head of the school's paper and Dixon's best friend, who paid for her rehab. Although at first she only does it to "repay" him, they start to genuinely care about each other. Adrianna later discovers she is pregnant as a result of her promiscuity while she was addicted. After telling Navid of her pregnancy, he breaks up with her. It is later revealed that the father of Adrianna's child is Ty, although it is unclear when they slept together. She and Navid get back together when he realizes that even though she is a mess he can't get over her, and get engaged, although he alienates his family when he tells them that the child is not his and gets upset when Adrianna reveals her daughter is Ty's.
Another featured character is Erin Silver, Kelly Taylor's half sister and Naomi's former best friend, until Silver's father's affair is revealed. She quickly befriends Annie and starts dating Dixon, who is somewhat taken aback by her not-so-90210 lifestyle, as she is a virgin who doesn't care about popularity. In a multi-episode arc that culminated in a very special episode, it is revealed that Silver has bipolar disorder. Kelly Taylor is now a guidance counselor at West Beverly and has a son named Sammy. She briefly dates Ryan before leaving to work on her relationship with former boyfriend and father of Sammy, Dylan McKay. This briefly causes friction with Brenda Walsh as both struggle with their lingering feelings towards Dylan. When Kelly returns, she not only discovers Ryan's relationship with student/cop Kimberly but also that he slept with Brenda, re-creating the rift between the two friends. Following Brenda's discovery that she cannot have children, however, the women are drawn together in an accord once again. Donna Martin, who has become a well-known fashion designer in Japan, is recently separated from David, and she decides to move back to Beverly Hills.
At Naomi's and Jen's (her sister) party, Liam sleeps with Jen. He is mad that Naomi told Jen about his past: he wanted to keep it a secret. However, he did not know that Jen was Naomi's sister, and upon finding out is horrified. Naomi finds out about it but thinks that Annie was with Liam, not Jen. This culminates in a major fight between Annie and Naomi where Annie runs a way, gets in the car drunk, and accidentally runs over a man.
Season 2 begins with the end of summer school for Dixon, Silver, and Naomi. Naomi unknowingly dates a married man in an attempt to get over Liam, who shows up at West Beverly on the first day of school. Silver and Dixon get back together, but break up soon after Silver receives a text message from Ethan revealing the two shared a kiss on prom night. Silver later reveals that she feels relieved upon learning Ethan will stay in Montana, and she still loves Dixon. Adrianna is desperate to become a normal teenager, giving up acting and, much to Navid's dismay, sex. Their relationship is put under further pressure with the arrival of Teddy, Adrianna's old boyfriend (who Adrianna lost her virginity to). Meanwhile, the emotionally distant and guilt-ridden Annie has cut herself off from all of society as much as possible, contributing to a growing disconnect between her and her brother, who is angry at her for sending him to summer school. Annie has kept her hit-and-run under wraps but learns through a private report that the unidentified victim, who had been in a coma, has died. At a end-of-summer beach party, Annie drinks away her worries with a senior, Mark, who later takes nude pictures of her. Naomi sees the photos and sends them to everybody at school as an act of revenge, as she believes Annie slept with Liam. Dixon, sick of Annie's drama, becomes even more distant.
Later on Annie dates Jasper (the nephew of the Hit-And_Run victim). What begins as a guilt-ridden friendship turns into a relationship. Dixon meets a girl named Sasha to whom he lies about his real age. Navid and Adrianna's relationship continues to hit rocks when Adrianna continues to show appreciation to Teddy. In the meantime, Harry and Debbie face marital problems when Harry confides in Kelly about his family troubles. Naomi finds out that her SAT scores are not high enough to get into California University so she decides to date the Dean of Admission's son, Richard. Later on she falls for Richard's roommate, Jamie. Sasha finally learns about Dixon's real age when Debbie accidentally shows Sasha, whom she did not know, a picture of her son Dixon who is only in high school.
Silver accompanies Adrianna to an AA meeting where she sees her mother Jackie, who has tortured her over the years. After Jackie apologizes, Silver insists on her mother leaving her alone. After a phone call from Adrianna, Silver learns that Jackie has breast cancer which shocks both Kelly and Silver. Kelly forbids Silver on seeing their mother to try to cover the pain, but Silver moves in with her mother to take care of her. Adrianna breaks-up with Navid to go into the arms of Teddy, but learns that Teddy does not want a relationship, which makes Adrianna feel sorry for the mistake she has made. Jen continues to manipulate both Naomi and Ryan, by making Naomi give her a large amount of money, and by making Ryan believe Liam is hitting on her. Silver being paired up with Teddy learns that Teddy's mom died, which causes a friendship to blossom. Sasha then tells Dixon that she is pregnant, at which Debbie and Harry think she is lying. Jasper convinces Annie to steal a car from the beach club to film his movie. Liam meets Ivy, a surfer chick whom he butt heads with. Later on they form a relationship. Navid and Gia launch an investigation, believing that Jasper is a drug dealer. Being upset about her break-up with Navid, Adrianna relapses on drugs. Liam has given up on Naomi and takes out Ivy to the Edison.
After Dixon confesses to Debbie and Harry about Sasha's pregnancy, Debbie meets Sasha and she finds out that Sasha is not really pregnant and advises her to stay away from her son. Sasha lies to Dixon saying she had a miscarriage, at which Dixon feels guilty for not being there for her, and then Debbie trying to comfort him agrees with Sasha's lies. Then she reveals the truth about Sasha which causes Dixon to get further away from his family. Jackie and Teddy give Silver the half-birthday of her life, by recreating her previous half-birthdays Jackie couldn't attend because of her alcohol issues. Navid sees Adrianna buying drugs from Jasper which causes him to confront them. Annie and Jasper confess their love for each other. Liam finally confides in Dixon, Teddy, and Ivy about the events on prom night as they try to figure out on a way to earn revenge on Jen. Their attempt to earn revenge on Jen works, which makes Jen lose everything she has including her sister and boyfriend Ryan. Teddy begins to pursue Silver more and they share a kiss on the roof top of the school.
Jasper pushes Navid down the steps because he finds out he is telling people that he is a drug dealer. Teddy asks Silver to the dance, but she says no. Navid suddenly remembers it was Jasper who pushed him down the stairs and is determind to let Annie know he is a drug dealer. Navid asks Adrianna to admit to Annie that she bought drugs from Jasper. After Dixon realizes that Jen is the one who slept with Liam and not Annie, he wants to help Annie. Naomi also feels bad for Annie when she learns the truth about prom night. At the dance, Teddy and Silver share a kiss. Silver storms off but later admits to Naomi that she felt something when they kissed. Just as Silver is about to tell Teddy that she wants to give it a shot, she sees him hugging a girl, not knowing it is Teddy's sister. Naomi, Navid, Dixon, and Silver reveal to Annie the truth about Jasper with help from Adrianna. Dixon forgives his mother and they are close again. Dixon reveals he still has feelings for Silver when he lies and says he didn't know who that girl was that Teddy was hugging. He kisses Silver. Ivy texts Naomi and tells her to go over Liam's house. Liam opens up to Naomi and they kiss. Annie confronts Jasper about his lies and he reveals to her he knows she killed his uncle.
After the mid-season break, the show returns on March 9, 2010 with the recurring episode entitled "Rats and Heroes". The students came back from their vacation, Naomi and Silver from St. Bart's and Annie from Las Vegas. Navid is determined to reveal Jasper's true ways. He comes back to school with cocaine he got from Berkeley. He wants to frame Jasper by planting it in his locker, but Navid's plans backfires when Jasper finds it first and somehow plants it in Navid's locker. Jasper continues to keep Annie close to him, while everyone questions how she can be with a guy like him. With Jen gone, Naomi and Liam are free to begin their relationship anew. They soon realize they have nothing in common, but Naomi is determined to make it work by pretending to be the kind of person she thinks Liam will want. Dixon and Teddy are into Silver again now that she has recovered. Silver likes Teddy, and wants to give him the benefit of the doubt that he is over his playboy stage. Dixon convinces both of them that they are not into each other. Adrianna reaches out to fellow Alcoholics Anonymous member Gia (Rumer Willis) for help with staying sober. To make Gia's ex-girlfriend jealous, Adrianna kisses her. Adrianna and Gia become good friends and later, when Gia reveals her feelings for Adrianna, they become a couple, but break up after Gia cheats on Adrianna with her ex-girlfriend. Silver and Teddy decide to be more serious about their relationship. Naomi admits to Liam that she has been pretending and that she needs to be true to herself, even if it means the relationship won't work. This is what Liam truly wants, and their relationship becomes more stable. However, when Naomi is forced to come clean over false rumors she spread claiming that she was sexually harassed by a teacher, Liam decides that he needs a break from her. During this time, Annie and Liam become closer and he consoles her after she overhears her mother, Debbie, confessing to her father, Harry, that she kissed her yoga instructor. His consolation causes Annie to believe that Liam is flirting with her, but realizing that this was not his intent, Annie instead advises Liam to stay together with Naomi. Regardless of her own advice, Annie continues to flirt with Liam, drawing his interest. In the finale, it's suggested that Naomi is sexually assaulted by Mr. Cannon, for real. He is very bad and intense. He said that she was the girl who cried wolf, and no one would ever believe her. What he doesn't know is that Mr. Matthews was outside the school and saw them both, but he was very drunk at the time.
The CW has renewed the show for a third season, which will air in fall 2010. 90210 will now air on Monday nights before Gossip Girl.
In an interview with E!, McCord revealed what she expected for Naomi after she was attacked at the end of Season 2.“ I kinda feel like there will be some downward spiral in a way for Naomi's character, but she's good at covering, so she'll still have that facade. ”