Andi's world turns upside down when her older sister, Bex, returns home on her 13th birthday and / Andi Mack has been raised to live on the safe side, but on her 13th birthday a revelation jumpstarts her path to self-discovery. At every twist and turn, she's anchored by her loving albeit complicated family and her loyal best friends, Cyrus and Buffy. Andi's life is further complicated by the arrival of her older sister, Bex, who has a secret that changes both their lives forever. As she determines where she fits in, and the many amazing ways she can live her life, she quickly learns that sometimes the unexpected is what truly makes life great.

Against Celia's wishes, Bex convinces Andi to stay up late to watch a scary movie; and when Andi falls asleep in class the next day, she receives detention and then misses the Space Otters game. Meanwhile, Buffy joins the track team and is determined to win.