A body is washed ashore badly cut after hitting rocks. Unrecognisable, the post-mortem reveals he had drowned in fresh water. Who is he and was he murdered? Using an artist's reconstruction to appeal locally for information, the police discover his name and address. Inquiries with his solicitor suggest he knew he might be killed. The letter left for the police also reveals he was a special agent working for President de Gaulle, hints at who may be involved and leads the police to find a safe that was hidden underground in his garage. When the safe is opened a decorated wooden block is found that appears to be solid. The beautiful object is covered with mother-of-pearl Arabic writing that is translated as Mohammed is the Prophet of Allah. The School of Oriental and African Studies at London University reveal the object is known as The Caliph's Great Seal and is believed to contain the only portrait of the Prophet Mohammed. How can it be opened? X-raying the Seal at Manchester University's Chemistry Department, at an ultra-low temperature, reveals a mechanism involving ten sprung levers that when pressed in the correct order will open the box. Further investigations find the artefact was acquired by Abdullah Quilliam, Britain's first and only Sheikh of Islam, from the last Caliph, Mehmed VI in 1924. How did the tablet find its way to an isolated house in the Isle of Man? When it is realised the tablet's value is priceless, but so dangerous that it could unleash a war between rival factions of Islam, what can be done to ensure its safety?