A mysterious Catholic priest arrives at 221B Baker Street, only to utter the words 'il corpe' before dropping dead. Though the man's death is attributed to cholera, when news of a similar case in Bristol reaches Holmes, he becomes convinced that the priests have been poisoned. He and Watson learn that the men were on a mission from the Vatican to investigate a miracle; it is said that the body of an eighteenth-century philanthropist and slave trader Edwyn Warwick has not decomposed. But should the Pope sanctify a man who made his fortune through slavery? And when Warwick's body is stolen, it becomes clear that the priests' mission has attracted the attention of a deadly conspiracy...