Four horses with little record of success suddenly won in the US. A seemingly coordinated betting operation across London did too – and now racing authorities want answers

To understand why horse racing on both sides of the pond has been gripped by the Fair Hill Five over the past week, start with a basic principle of betting: when two unlikely horses win in back-to-back races, a wager correctly picking both should pay off handsomely. Last Sunday at New Jersey’s Monmouth Park, it did not.

The sequence began with The Great Amira, a 17-1 longshot who went from finishing last in her previous two starts to winning wire to wire by nine and a half lengths. Her little-known trainer then won the very next race with Tepeyac, who went off at about 4-1, and the meager Daily Double payout for picking both outsiders suggested the exact combination had been unusually well backed. Later that afternoon, two more longshot winners emerged at Saratoga. They were among five runners with recent workouts at Maryland’s Fair Hill Training Center, the common link behind the name Fair Hill Five.