Tara Gregson is a wife and mother of two. Tara has dissociative identity disorder (DID). Whenever she is stressed, she transforms into one of her alternate personalities: wild and flirty teenager T; old-fashioned housewife Alice; and male, loud, beer-drinking Vietnam vet Buck (a fifth personality is introduced later in the season). Tara is supported by her husband Max, her somewhat troubled teenage daughter Kate and quirky, good-hearted gay son Marshall. Her sister, Charmaine, is not so supportive, often expressing her doubt about the validity of Tara's disorder.
Max is worried when Tara returns to college to finish her college degree. Meanwhile, Charmaine with a baby on the way is avoiding a commitment to Neil, Kate tries to figure out a plan for her future and Marshall and Lionel sign up for a filmmaking class.
Her psychology professor humiliates Tara when she transitions in his class. Meanwhile, Kate considers giving English lessons in Japan and Max gets a business offer.
The stress of juggling school and Charmaine's baby shower causes Tara to transition, with negative consequences for Charmaine. To sell the family business, Max must get the approval of his eccentric mother. Kate meets a flight attendant who inspires a new idea about her future.
Tara and Charmaine are rushed to the hospital in the same ambulance, where Charmaine declares her baby off limits to her crazy sister; Tara attempts to make a deal with her alters, which intrigues her Abnormal Psychology professor; Marshall, Lionel and Noah put Charmaine's empty house to some creative uses; Kate is embarrassed to confess that she backed out of going to Japan.
Tara tries to drop her Abnormal Psychology class but instead receives an intriguing pitch from her instructor, Dr. Hattaras; Charmaine and Neil find parenthood a struggle but still refuse Tara's help; Max finds himself at odds with his boss at his new job; Kate prepares for flight attendant training; Lionel catches Marshall with Noah, jeopardizing their student film project.
Tara seems to be making progress with her new contract but Dr. Hattaras discovers something disturbing in a tape from one her therapy sessions; much to the sisters' chagrin, Neil invites Tara and Charmaine's mother to visit her grandchild; Max is unhappy at his new job but can't talk to Tara about it; Kate is surprised when a handsome flyer rebuffs her flirting.
Tara motivates Max to relive his old rock band Beaverlamp. Meanwhile, a depressed Dr. Hattaras makes her take a break from their therapy sessions and Marshall and Noah interview Max for their film festival project.
A new alter comes to light that puts Charmaine's new baby at risk. Soon after, Alice visits Dr. Hattaras and intrigues him in Tara's case again. Kate, Max and Marshall fly to New York where they get to meet Kate's new friend Evan and his son.
The discovery of Tara's new dangerous alter makes Dr. Hattaras and Tara consult another professional. Marshall finds out that his short film hurt his father's feelings and Charmaine connects with "chic moms," while Kate tries to make her relationship with Evan work.
Max and Marshall return home from New York to bad news on all sides. Max learns of the new alter, Bryce, but a highly medicated Tara assures him all in under control. Marshall learns that a close friend has been killed in an accident. Tara offers support, which he gladly accepts, but on the day of the funeral Bryce emerges and apparently will not go away. It's all too much for Kate and Marshall who look to strike out on their own.
When Bryce takes over, Tara's new alter threatens to destroy the whole family. When Tara's other alters disappear one by one, Max decides to fight off Bryce before it's too late for Tara.
Tara re-emerges but the task now is to repair broken family relationships, particularly with Marshall who is fed up with it all. Rather than go into a local mental health facility, she decides to follow Dr. Hatteras' advice and see a specialist in Boston. Neil and Charmaine are moving to Houston and offer to take Marshall with them. Kate receives an offer to move to St. Louis. As a new family dynamic emerges, everyone contemplates and wonders what the future may hold.