Jennifer Mills, a 25-year-old played by Anna Chlumsky, enjoys a commitment-free life and is glad her boyfriend isn't thinking about marriage. Unlike her older sister Mandy (Chelah Horsdal), who married young and embraced family life, Jennifer prefers her carefree lifestyle. However, her mother Kathryn (Susan Hogan) believes Jennifer's reluctance to settle down stems from fear and devises a plan to change her ways in three weeks. When Mandy and her husband go on a three-week European trip without their three kids, Kathryn persuades Jennifer to babysit them until she arrives. Jennifer soon discovers that taking care of children is no easy task and realizes she needs to transition from the fun aunt to a responsible guardian to maintain her sister's trust. With some assistance from Will (Warren Christie), the attractive new neighbor, she manages to prove that embracing responsibility can be fulfilling.