Gamble

Nick Foxton once won the Grand National, but a fall put an end to his racing and now he's just a spectator at the big event. And right now all he can do is watch as his friend Herb Kovak is shot dead in front of him, the killer vanishing into the crowd.
The police want answers but Nick has no idea why anyone would want his friend dead. Not until he finds the crumpled note in Herb's coat - a cryptic warning.