Christine's 8-year-old son, Ritchie has been accepted into a posh private school where Christine encounters two snooty class moms, Marly and Lindsay, who can't seem to grasp the concept that Christine actually works. Her 20-something slacker brother, Matthew, lives with her, but in a pinch, also serves as Ritchie's babysitter. On the first day at Ritchie's new school, Christine is mortified to discover that her ex-husband, Richard, with whom she gets along even better than when they were married, is dating a young, nice, impossible-to-hate woman also named Christine… the "new" Christine.
When Christine learns that Richard and "new" Christine are enjoying an intimate relationship, she becomes determined to make her own conquests. After several failed attempts to meet eligible men, she finally runs into a guy named Stan at the grocery store. Unbeknownst to Christine, Stan is a father at Ritchie's school who is known as "Sad Dad."
When Christine learns that her close friends, Barb and Pete, are responsible for introducing Richard to his "new" Christine, she allows them to set her up on a blind date of her own. After a series of unsuccessful dates, she finds the possibility of love in the strangest of places. Meanwhile, Matthew takes Ritchie to swimming lessons.
Richard learns from a gloating Matthew that Christine is out enjoying her fifth date with a new beau, Burton, so he does what any self-respecting ex-husband would do: he sabotages the happy couple's goodnight kiss and insults Burton with lawyer jokes. But when he tries to make it up to them by inviting Christine and Burton to dinner with him and "new" Christine, his best-laid plans go awry.
After 10 dates, Christine faces a critical moment in her relationship with Burton. Will she or won't she? Let him in the house, that is, to meet her son, Ritchie. She eventually relents, only to be thrown for a loop later.
Concerned about the uniformity of Ritchie's schoolmates, Christine takes it upon herself to help diversify the student body at his private school.
Following Christine's breakup with Burton, everyone expects Christine to fall apart emotionally, but she insists she is fine and looking forward to spending time with her best friend: "me." But after being humiliated while dining out alone, Christine realizes she really did care for Burton, which drives her even crazier.
Christine feels pressured to throw an extravagant party for Ritchie's 9th birthday, his first involving other children from his new private school. Recoiling from sticker shock after meeting with a ritzy event planner, Christine decides to have an arts and crafts party at her home, with mixed results.
Christine tries not to have a meltdown when her ex-husband, Richard, brings his "new" Christine with him to pick up Ritchie and take him to breakfast so that they can get to know one another. By day's end, Christine tries to pull herself together to make a good impression at parents' night at Ritchie's school, but is caught off guard when "new" Christine shows up as well.
Christine's former marriage counselor comes into the gym, leading to some awkward moments between the two women. When Christine mentions this to Richard, his cryptic reaction leads her to question whether it was in the counselor's best interest to encourage their divorce. Meanwhile, Matthew finds Christine's wedding video in a box of old photo albums, and Christine takes a trip down memory lane.
Christine objects when Richard and "new" Christine want to take Ritchie to a Rolling Stones concert. Fearing that Ritchie is too young to be exposed to sex, drugs and rock and roll vices on display at a Rolling Stones concert, Christine initially forbids it. Eventually, she relents but immediately regrets her decision and, in a panic, goes to the venue with Matthew to see if she can sneak into the concert in order to keep tabs on Ritchie.
Shut out once again by the cliquey, judgmental moms at Ritchie's school, Christine runs into a down-to-earth working woman, Belinda, who invites her over for a drink after work. Belinda's job, however, isn't quite the type of position Christine expected her to hold, which throws yet another wrinkle in her attempt to fit in with the other school parents.
Christine volunteers to help out at Ritchie's spring carnival and while there, she runs into the mean moms -- Marly and Lindsay -- who are clucking over the attractive father of a new student at Westbridge. Christine is excited to learn that the hot dad is her ex-boyfriend, Burton, but her hopes of re-igniting their romance are shot down when she learns Burton has a new girlfriend.
Since "New" Christine broke up with Richard, he's been spending a lot of time at her house, leading Ritchie to believe that his parents are back together. When Christine tells Richard that Ritchie told this to his new teacher, Mr. Harris, Richard suggests that they give their relationship another try.
Richard tells Christine that the reason he has good luck with women is that he "says yes to life." When Christine meets a good-looking man after paying a surprise visit to New Christine, she decides to break out of her mold and says yes when he asks her out to dinner.
Christine is stunned to find out the man she's seeing, New Christine's father, is also a grandfather.
Ritchie goes to church with Richard and new Christine without consulting his mother first, leaving old Christine to explain and explore her aversion to organized religion.
Barb moves in with Christine after deciding to divorce her husband. This forces Matthew into Ritchie's room, where he discovers his nephew has some odd habits.
Christine runs into Stan again and is unable to resist him, despite her best efforts. She asks Matthew to help keep Stan away from her, but her brother is having attraction issues of his own--his latest girlfriend refuses to leave.
Christine's attraction to Ritchie's teacher causes a scene at a school fund-raiser--especially after she wins a playdate with the man.
Christine makes sacrifices so she can pay for Ritchie's school tuition.
After Richie begins showing more interest in spending time with Richard and then does a bad job on his school homework project, Christine contemplates bailing Richie out in an attempt to win him over again.
Christine has trouble working with Barb at the gym and feels pressure at home to find a nanny for Ritchie when Richard is unavailable to care for him due to a trip with New Christine.
When Christine's environmentally-friendly hybrid car and Marly's gas-guzzling monster SUV hit one another, it becomes a bigger dispute than simply who hit whom. While her car is in the shop, Christine is forced to go against her principles and rent a luxury SUV when no other car is available.
Richard want Ritchie to learn the value of competition and male bonding, and signs him up for soccer. Christine disagrees, but then has her own competitive urges when fighting with Richard for attention from Mr. Harris.
Christine can't help but meddle in Matthew's love life when she meets his ex-girlfriend at a party. Meanwhile, Richard hopes to get Ritchie enthused about his contracting job.
Jealous that New Christine benefits from all the positive qualities she instilled in Richard during their marriage, Christine spites her by revealing to Richard that she gave New Christine the idea for the birthday gift she gave him.
Christine finds out her new sleep medication caused her to embarrass herself over the phone.
Christine finds out Richard's brother is gay, but not until after sleeping with him.
Christine vows to become more aware of politics when Richard scolds her about her indifference towards an upcoming election setting a bad example for Ritchie.
Trying to send an e-mail to Barb about Mr. Harris, Christine ends up sending it to all the parents from school, nearly costing him his job.
When Christine learns that Richard has been hired to remodel "meanie mom" Lindsay's bathroom, she can't help but intervene to make sure he doesn't screw up the job and risk their reputation at Ritchie's school. Additionally, she and Richard are at odds over which of them gets to be the one to give Ritchie the sex talk.
The stresses of going to a wedding with Richard and Barb are multiplied by Christine's agreeing to be designated driver, depriving her of some much-needed alcohol.
On their way to Ritchie's desert camping trip, Christine, Richard, Matthew, and Barb stay at a seedy motel and get on each others' nerves.
Christine realizes that one reckless evening may have jeopardized her chance to begin dating Mr. Harris.
