https://www.goodreads.com/book/show/5...

The same Halloween night park ranger, Bill Steward, hears the terrifying cry of a child out on the moors of Old Castle's national park, cemetery caretaker, Old Man Cronin, is carrying out a macabre yearly ritual. The only difference is that this year's ritual will be his last.

Seven autumns later, Bill’s life is turned upside-down when he discovers a highly unusual medical prescription in a child’s handwritten scrawl.