A woman whose vision of a perfect life with her adoring fiancé, Nick, and his wonderful family is radically altered when her 16-year-old, out-of-control half-sister, Shannon, unexpectedly comes to live with them.

During their engagement party, Clem and Nick are both shocked to learn that the other has been keeping an embarrassing secret about how they met.

When Clem and Nick run into Nick’s ex-girlfriend at their hotel during a romantic weekend, Clem is upset to learn that Nick and his ex once lived together in the same apartment they live in now. Also, Shannon’s friend tries to persuade her to throw a big party while Clem and Nick are away.

Clem feels her former “fun” life slipping away after attending Shannon’s school’s Open House and joining the PTA, and decides to liven up the low-key bachelorette party she originally asked for.