While attending a meeting to get Ritchie into a new school for seventh grade, Christine gets in trouble when she runs into a man who spread some dirty rumors about her when they were in seventh grade themselves.
Christine and Barb give New Christine a bachelorette party in Las Vegas, where New Christine lets all of her previous inhibitions go. Meanwhile, Richard, Matthew, and Richard's brother spend Richard's bachelor party playing laser tag.
Barb and Matthew both move out of Christine's house at the same time, so she tries to prove to everyone that she can make it without them. But was Matthew's decision to move in with his girlfriend a good idea?
Christine makes friends with a woman who is as needy and dependent on her as she is on Barb, and Matthew has a bad experience moving in with Richard and New Christine.
There is an outbreak of lice at Richie's school and he is one of the affected ones. Everyone thinks Christine and Richie are "patient zero". Tired of the hassles at that school, Christine looks for another school for Richie.
Christine and Matthew try to lose weight together, but only Matthew is successful. Meanwhile, Ritchie tells Richard that he doesn't want him to marry New Christine.
Christine tries to convince herself that her date for Richard and New Christine's rehearsal dinner isn't a total jackass, while Matthew hooks up with New Christine's sister.
Christine hooks up with New Christine's dad again before the wedding--and then finds out he's getting married. Also, Matthew finds out his new relationship is temporary, and Barb's new potential beau is forced to arrest her.
Barb and Matthew visit New Christine, but only manage to get her angrier with Richard. Meanwhile, Old Christine and Richard's reunion with some old college buddies does not go as planned.
While Richard and New Christine reach a stalemate over who gets to stay in the house, Old Christine has a horrific experience as an uninsured health care patient.
Right before Barb is to marry Richard to avoid deportation, Christine sues Barb for alimony. Meanwhile, Marly and Lindsay ask Matthew to be their new "therapist."
Christine gets fired as Matthew's temporary secretary, and then develops a romantic interest in his mentor. Meanwhile, Richard and New Christine's new arrangement becomes more complicated.
Christine considers herself popular by association when Ritchie is asked to a dance by the most popular girl in school, and Matthew and Richard try to evict an elderly woman from the apartment they hope to rent.
Max points out to Christine that she quits anything that gets too hard, including relationships, which is one of the reasons he chose to be her therapist rather than her boyfriend.
Christine sets Richard up on a date with a gorgeous, passionate woman who works out at her gym, while Richard's friend, Tom, continues trying to woo Christine.
Barb asks Christine to join her on a date with Dave, and Christine insists that Richard "woo" her if he expects their rekindled relationship to survive.
Christine only makes things worse when she tries to make amends to a girl she bullied in junior high, while Matthew has a surprise in store for him when he tries to "friend" an ex-girlfriend on Facebook.
Christine and Matthew reluctantly attend a neighbor's Christmas party, while Richard and Ritchie participate in New Christine's unusual holiday tradition.