Billy's Experiment: An Old Castle Audiobook

Billy's Experiment audiobook. BOOK 2 of The Old Castle Series. This series can be listened/read in any sequence.
READ BY THE AUTHOR
A dark tale of mistaken identity...
On the night of a lunar eclipse, park ranger Bill Steward rescues a baby from a strange band of misfits on the misty moors of Old Castle's national park.
Seven autumns later, Bill and his wife, Dorothy, discover a ghastly experiment in a treehouse and a mysterious medical prescription written in a childish scribble. 
Bill realises what he'd observed on the moors seven autumns ago wasn't what it seemed. Who was saving who, exactly? 
Just as Bill's eclipse is beginning, so, too, is Billy's.