Bogey's Mortal Lock by John Meeks

Bogey Dawson and Becky Friedman were breathing easy. Edmond Huddleston's effort to kill them ended in his own death. Their talented race filly Final Gift was headed for the Kentucky Derby as one of the favorites. But when things go wrong in the Derby, it's only the beginning of a blur of danger and misfortune that pulls them into a vortex of evil beyond anything they could have imagined.