1795, and a young woman travels in haste from Cambridge to the Suffolk coast. Her name is Mary Finch, and she has been invited to meet her wealthy uncle - and so end a family estrangement that has held fast for more than twenty years. Smart, courageous and blessed with good looks if not good fortune, Mary is excited by the prospect of adventure, and the chance to escape a miserable future teaching at Mrs Bunbury's school for young ladies. But a whispered warning from a man dying on the road who carries a strangely familiar watch bearing her uncle's initials, exposes her to a ruthless conspiracy that threatens not only her family's reputation, but her very life. With England embroiled in a bloody war with Republican France, and spies and smugglers active all along the coast, Mary must learn quickly how to fight for her survival, and to distinguish friend from foe. Can she trust the two men who want to help her? What is their interest in the mysterious Blackstone key? Does it guard a secret treasure, or might it have a more sinister purpose?