The only worries twenty-one-year-old Olivia Martin (Lacey Chabert) has to deal with are midterms, finals and what to wear to the next fraternity party. But when her father and stepmother are tragically killed in a car accident, Olivia suddenly finds herself responsible for her seven-year-old half-sister she barely knows. Olivia reluctantly accepts custody of Celia (Sammi Hanratty) and discovers becoming a family will be a lot harder than she ever imagined. With the help of her self-involved and capricious mom Barbara (Wendie Malick), Olivia and Celia begin to give each other a chance and learn to trust one another. But when caring for Celia takes a toll on Olivia's social life and she begins to miss her freedom and carefree days, will she experience a change of heart?