They say the third time's the charm, and reformed party girl Kate is hoping that's true when she becomes the third wife of a slightly older man, Pete. They fell into each others' arms (literally) at a karaoke bar, and flash forward a year later, Kate finds herself with an instafamily complete with three stepchildren and two ex-wives. But Kate is determined to make this work and become a part of the family no matter what.
When Kate falls in love with the man of her dreams, she finds herself in over her head juggling her new responsibilities and new relationships with his three children and two ex-wives. After embarrassing herself at a parent-teacher conference, Kate makes a bold move to help her stepdaughter hide a secret. Meanwhile, Pete and Jackie conspire to hide the death of a pet hamster, and Bert bullies Meg into buying him a new Lego set.
When Kate asks for more responsibility, Pete has her help him coach Bert's soccer team; Warren and Hillary stain Diane's couch.
When Hillary starts sneaking around on the weekends, Pete overreacts and makes matters worse. Kate tries to take over, but she finds that her own parental style needs work.
When Meg needs Kate's help getting through a breakup, Kate finds herself torn between her obligations as a friend and her responsibilities as a wife and stepmom. Kate struggles to be a good friend to Meg, but when Meg's breakup drama gets to be too much, it leads to a falling out between them.
Finding it more and more difficult to spend time alone and away from Diane's constant demands, Kate and Pete sneak away for a romantic tryst at the school fundraiser. But when they get trapped, truths come out and Kate reveals she wants to be at the top of Pete's priority list and for him to stand up to Diane
When Jackie's homemade costume nearly ruins Bert's Halloween, Kate steps in with the costume he wanted, and Bert's so overjoyed that he asks Kate to take him trick-or-treating. This leads to a fallout between Jackie and Kate, which gets worse when Bert goes missing.
When Jackie has a drunken encounter with one of Pete's coworkers at Kate and Pete's party, Kate and Pete deal with the ensuing awkwardness. Meanwhile, Warren and Bert try to attract more viewers to their live-streaming gum show, and Meg helps Diane with a secret mission.
When lice attack the Harrison household, Kate and Jackie band together to show Diane that she isn't great at everything she does. Meanwhile, Warren and Bert fight about custody of a teddy bear.
Kate tries to play matchmaker to Diane and another parent on Warren's field trip, but is shocked by what she learns in doing so.
When all the presents go missing on Christmas morning and none of the parents can remember where they are, the family goes on a mission to piece together the mystery of what happened the night before Christmas. Along the way, Kate and Jackie team up to give Diane the perfect Christmas gift and Pete trades in his Grinch-like attitude and embraces the true spirit of Christmas.
Kate tries to break Pete's lifelong streak of horrible birthdays, but it seems the curse is very hard to break. Meanwhile, Diane and Jackie spend the day together looking for a birthday gift for Pete.
When Warren and Hillary misbehave on Kate's watch, Diane convinces Kate to actually punish them for once. Kate lays down a harsh sentence... which the kids are able to exploit to "punish" her.
When Bert loses a tooth, Kate learns of Pete and Jackie's elaborate Tooth Fairy rituals. The fact that Kate doesn't share their excitement makes her question her maternal nature.
Jackie pitches a business idea to Pete, which he dismisses because of her poor entrepreneurial track record. But Kate thinks it's a good idea and partners up with her.
Kate uses Bert's birthday party as an entree into the exclusive soccer mom clique.
When Kate finds Pete's old wedding videos, she realizes she wants a wedding of her own. But as the preparations begin, Kate discovers she's in the country illegally.
Kate persists in planning her dream wedding despite the added chaos from the arrival of her mother Cricket (guest star Megan Mullally) and Pete's parents.
In order to get some time to themselves, Pete and Kate lie to Jackie and Diane about being in couples' therapy.
The Kate-Diane power balance flips after Kate publicly saves Diane's life. But when a now over-confident Kate gets in trouble at the PTA meeting, she needs Diane to help get her out of it.
Kate tries to help Warren improve his social life, but her efforts backfire.
Kate begrudgingly agrees to accompany Jackie to her high school reunion, not fully realizing all that it entails.
Kate is overjoyed when Diane and Jackie offer to let her have the kids on her first Mother's Day, however, when Kate discovers their hidden agenda -- she is determined to get revenge.