The Trojan Colt — Mike Resnick

Hired to guard a high-priced yearling of "Trojan," a recently retired classic winner in Lexington, Kentucky, Eli Paxton is only days into the job when the yearling's young groom goes missing.  Asked by the boy's parents to investigate his disappearance, Paxton focuses on the Lexington breeding farm. It turns out that another staff member has disappeared in the past couple of months. As Paxton worries that the missing boys may never be found, he becomes a target himself when a secret threatens to derail the world of professional horse racing.