A failed murder by arson after a string of successful ones exposes more than a criminal's mistake; it reveals the hidden life of a Catholic priest in exile and his journal, which hints at a mysterious ancient manuscript shrouded in centuries of secrecy.MI5 Inspector Andrew Hamilton is assigned to unravel the mystery and find out who is behind the killings. To do so, he must work with his estranged ex-girlfriend, Professor Karen Wesley, an expert in religious history-and the last person he wants by his side.Their uneasy alliance draws them into a deadly game involving an Arab businessman with shadowy motives, a clandestine Catholic society guarding long-buried secrets, and a violent faction obsessed with Nazi revenge. From London's backstreets to a road leading to Glastonbury's sacred ruins, Hamilton and Wesley race to uncover the truth behind the Tin Merchant's Riddle before the next fire consumes them all.