Dick Francis's Damage
(Book)

"Undercover investigator Jeff Hinkley is assigned by the British Horseracing Authority to look into the activities of a suspicious racehorse trainer, but as he's tailing his quarry, Jeff bears witness to a bloody murder. Could it have something to do with the reason the trainer was banned in the first place--the administration of illegal drugs to his horses? Soon it's discovered that many more horses have tested positive for stimulants--and an unknown person starts making demands, threatening to completely destroy the integrity of the racing industry. To protect the sport itself, Jeff must uncover the perpetrator. But he's up against someone who will stop at nothing to prevail"--