Eavesdropper By John FrancomeA trainer loses his licence; a jockey is warned off: all in a day's work for the senior steward of the Jockey Club. But when the blackmailing starts, when a most influential corpse is found in a horse box at Newbury races, a cloud of corruption, suspicion and violence threatens to overwhelm the National Hunt season. James Thackeray, racing journalist, erratic tipster, amateur jockey, had every reason to turn detective. He'd found the body. But it was