The subject of this book is an inscription carved on a stone slab which can be found built into the wall of a small parish church in Anglesey. The Latin inscription, called 970 Catamanus for short, has appeared in guidebooks and archaeological publications, but all these descriptions are incomplete because they fail to address the question of the slab's original nature and function. It has been widely supposed that the stone slab was a plain memorial, a lettered tombstone for a named Christian ruler - Catamanus, king of Gwynedd - but Thomas demonstrates that this is only part of the truth. In a creative attempt to unravel the mystery of the inscription Thomas appeals to Sir Arthur Conan Doyle for inspiration. He begins by exploring the world of a 7th century Welsh ruler, who, mindful of his dynasty's illustrious past and desirous of arranging his salvation after death, founds a new church, re-inters his grandfather's bones beside it, and arranges for a stone slab to mark the burial spot with a suitable inscription to honour his ancestor. He then goes on to investigate the Irish cleric who composed the inscription, secretly encoding in the letters vain self-references and scandalous innuendos regarding the hero's "true" character. Thomas leads us through the complexities of Christian symbolism, Roman letter-games, word patterns, and colloquial Latin, in order to expose the outrageous truth hiding within the inscription.