Found by Margaret Peterson Haddix

It wasn’t there.  Then it was.  Later, that was how Angela DuPre would describe the airplane—over and over, to one investigator after another—until she was told to never speak of it again.  The mysterious airplane arrived at gate 2B carrying only 36 babies, one on each seat.  13 years later, Jonah, one of the adopted babies, receives a letter in the mail with only six words on it.  You are one of the missing.

Confessions of a Murder Suspect by James Patterson and Maxine Paetro

When Malcolm and Maud Angel are murdered, the only suspects are their children, Tandy Angel and her brothers.  Tandy is a whip-smart prodigy and she’s got secrets, some of which even she doesn’t understand.  But she couldn’t have killed her own parents could she?  You tell me.  Does this girl look like a murderer to you?