"The Finder of Lost Things" is the name Blanche Wainfleet's three sisters bestowed on her when they were young, not only for her ability to locate missing handkerchiefs and runaway pets, but also because she was so good at finding solutions to all manner of puzzles. Now, in the winter of 1590-1, twenty-eight-year-old Blanche, a London merchant's wife whose husband is traveling abroad, is faced with a much more serious mystery, one she is desperate to solve.

Late Elizabethan England is an era rife with treason and conflicting political and religious loyalties. Priest-catchers target Catholic households in the hope of being able to arrest and execute priests. The householders themselves have to pay ruinous fines if they do not attend Anglican services. And yet leaders of both faiths agree that a bewitched person can be cured by exorcism.

When Blanche's youngest sister, Alison, fell in love with a Catholic gentleman, she converted to Catholicism and went to live at Otley Manor as Lady Otley's companion. Arrested for illegally hearing mass, she died under mysterious circumstances while imprisoned in Colchester Castle. Some say she was bewitched to death.

To discover the truth about how Alison died, Blanche contrives to have herself confined with Lady Otley and other members of the Otley household in Colchester's dungeon. She tells no one of her connection to Alison, but does pretend that she, like her sister, wishes to convert. Still without answers when a royal pardon sets all women prisoners free, Blanche accepts Lady Otley's invitation to join her household and take instruction in the Catholic faith. She's just begun to make progress when a second murder puts her in mortal danger from powerful figures on both sides of the religious divide.