Bonecrack by Dick Francis
At twenty to midnight Neil Griffon's home is broken into and he is roughly abducted by masked men. He has no idea who they are, or what they want. But when Neil wakes up, hours later, he quickly discovers that unless he cooperates his kidnappers will destroy his father's precious horses, racing stable and ultimately Neil himself.
Returned to take charge of the stables, Neil can tell no-one about his ordeal. Vicious threats and horrible violence against his horses become a day-to-day reality and he is forced to comply with his blackmailer's wishes. Trapped in a war of attrition, Neil realises he must find a way to stop these criminals before his nerve gives out. After all, a choice between his integrity and his life is no choice at all . . .