Though the man's death is attributed to cholera, when news of another dead priest reaches Holmes, he becomes convinced that the men have been poisoned. He and Watson learn that the victims were on a mission from the Vatican to investigate a miracle; it is said that the body of eighteenth-century philanthropist and slave trader Edwyn Warwick has not decomposed. But should the Pope canonise 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...