'It is one thing to say that you do not believe in ghosts and quite another to walk alone through the Abbey cloisters after dark...' Going through the cloisters one evening, Emily bumps into a stranger. In the gloom she cannot see who he is, but it seems that he wears a monk's habit, and has only a stump where his hand should be. Soon after this unnerving experience, Emily and her older sisters, Penelope and Alyce, are puzzled by the appearance in Westminster Abbey of a party of French monks, led by the enigmatic Father Pierre. Is their all-night vigil at the Abbey genuine, Penelope wonders, or is it in fact a cover-up for some illegal activity? Alyce's overwhelming interest in history leads to an exciting question. Was all the treasure once guarded in the Abbey actually discovered in Tudor times; or did some remain hidden - to tempt twentieth century thieves?