The Key to Rondo — Emily Rodda

THERE ARE FOUR RULES TO the old, painted music box that Leo Langlander inherits from his great-aunt: Wind the box three times only.

Never wind the box while the music plays.
Never move the box while the music plays.
Never close the lid till the music has stopped.

Leo wouldn't dream of breaking these rules -- he wouldn't dream of doing anything wrong. Then his weird cousin Mimi comes to visit, and the first thing she does is wind the music box four times. But what Mimi intends as a prank unlocks a hidden world -- and frees the sorceress inside it. Now Leo and Mimi must pair up to stop the witch -- if only they can discover the true secret of the music box in time.