Bones and Heart, the ebook short, will be included in the Thorn Jack paperback! It's Jack's origin story. When he's sent on a mission by Reiko (a month before Finn's arrival), to the sinister Fata Mr. Bones, a creator of Grindylow, Jack recalls his first encounter with the Fatas in London with his exorcist father.
There's also currently a Goodreads giveaway taking place for Thorn Jack!