Magic Tree House
Junie B. Jones
Elise and Franklin have always been best friends. Elise has always lived in the big house with her loving Uncle and Aunt, because Elise's parents died when she was too young to remember them. There's always been a barn behind the house with eight locked doors on the second floor.
When Elise and Franklin start middle school, things feel all wrong. Bullying. Not fitting in. Franklin suddenly seems babyish. Then, soon after her 12th birthday, Elise receives a mysterious key left for her by her father. A key that unlocks one of the eight doors upstairs in the bar . . .
From the Hardcover edition.