Theo Jennings is a young auctioneer at the Thoroughbred sales ring in Newmarket. The October yearling sales are where the big money exchanges hands in frenzied auctions: millions of Guineas paid for horses that are as yet unnamed, untested, and have never taken a step on the track. It's the greatest gamble in all of horseracing, and one that can end in ruin.

Theo has just made the biggest sale of his life, when he overhears a secret conversation between the two bidders - can they really have colluded to fix the price of his big sale? When that same horse is found dead the next morning, he has no choice but to investigate, even against the wishes of his boss. But the more he uncovers, the less he can trust the people around him.