Flying Fish by Dick Francis

When amateur jockey and pilot Lord Henry Grey launches himself into a career in the bloodstock market, he finds more danger and excitement than he'd ever anticipated. Henry immediately takes to his glittering new world and, when he meets the glamorous Gabriella in Italy, is sure he's hit the good life. That is, until a horse mysteriously dies in transit and a colleague vanishes. Then Grey discovers that both his predecessors went missing in mysterious circumstances and begins to doubt the wisdom of his career change. Either he has to turn detective or his own disappearance could be next ...