In 12th-century France, the power of the religious relic is unsurpassed.

Suffused with enormous power, a dangerous and violent trade has grown up around them. Despite mourning for their first child, the young ex-novice Catherine LeVendeur and her English husband Edgar are drawn into this perilous world when Edgar agrees to pose as a craftsman in order to infiltrate one if the rings.

The future of Catherine's relatives is also at stake: Jews surviving on the tolerance of King Louis VII. Their fragile existence is shattered when a man is murdered, and a deeply important relic - the arm of Saint Aldhelm of England - is stolen.