Up on Cloud Nine — Anne Fine

Ian's best friend, Stolly, is up on cloud nine. He's in the hospital, unconscious, and hooked up to machines. The question Ian is trying to answer is: How did Stolly end up there?

In a way, Stolly's always been on cloud nine, living life by his own rules and making those rules up as he goes along. His parents' careers have them constantly rushing around, so Ian's family has all but adopted Stolly. That's why it's up to Ian to figure out what happened to his best friend. But once the pieces start coming together, the answer doesn't seem to make any sense.