It Rides a Pale Horse by Andy Marino

Peter Larkin — Lark to his friends — is a local hero in the small town of Wofford Falls. The one who went to the big city, found fame in the art world, then returned home to settle down. He's the kind of guy who becomes fast friends with almost anyone. His sister, Betsy, is talented as well. And eccentric. Unlike Lark, she keeps to herself.

When Lark meets with a fabulously rich client, it seems like a regular transaction. Even being met at the gate of the sprawling, secluded estate by an intimidating security guard seems normal. Until the guard plays him a live feed: Betsy being abducted in real time.

Lark is informed that she's safe for now, but her well-being is entirely in his hands. He's given a book. Do what the book says, and betsy will go free.