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?