Andi Mack is turning thirteen, and she feels like her life needs a little shaking up. But when her wild and crazy older sister Bex returns home and tells Andi that she's actually her mom, Andi is, well... SHOOK! Will life as she knew it ever be the same? Then, Bex convinces Andi to throw a huge house party while the parents are away. It's all fun and silly string until mean-girl Amber shows up. Bum-mer! Can the Mack girls keep the good times going, or is their fiesta doomed to fail?