Black Dog Part III (A Chuck Wendig Challenge)

So this is part three to a scary story and where the rubber meets the road so to speak.

Part I is here: http://jemimapett.com/blog/2016/10/07/fridayflash-fiction-spooky-tales-1-black-dog/

Part II is there: https://kim153.wordpress.com/2016/10/19/scary-story-part-two-of-jemima-petts-story-black-dog/

Many thanks to Jemima Pett and Kim Blades for the setup.