Triple cross

the long version

"Although 23-year-old barn manager Steve Cline doesn't expect to stray far from the horse world, he has enrolled in a private investigations course and is working on the final project. But when his father, racehorse trainer Chris Kessler, invites him to Louisville on a two-week, all-expense-paid vacation that will culminate with the running of the Kentucky Derby, how can he refuse? Except, it isn't really a vaction. Kessler has a Derby runner and needs a reliable fill-in when one of his employees is injured"--Publisher website (May 2007).