It Took Billy by Miguel Lopez de Leon

The handwritten journal of a boy named Billy was found in a hollow tree trunk in the woods. The pages from the first half of the notebook had been ripped out. At the time the journal was discovered, Billy had been missing for three months. It Took Billy is a dark fantasy for adult readers. The story centers around the harrowing journey of a teenage boy who is abducted by an ancient demon, and thrust into a twisted world full of cruel magic, powerful mystics, and enraged immortals. Left with nothing but his notebook and a pen, Billy chronicles every detail of his terrifying ordeal. This is Billy's journal.