When a sacred reliquary vanishes from the Benedictine Abbey of Shrewsbury, Brother Cadfael must determine if the thief was motivated by greed or a misguided sense of religious devotion. Brother Cadfael, a monk with a background as a crusader and herbalist, applies his worldly experience to navigate the tensions within the monastery and the surrounding town. He faces opposition from those who view the theft as a divine judgment and from secular authorities eager to exploit the chaos. The narrative, presented in a third-person perspective, captures the rigid social and religious hierarchies of 12th-century England while focusing on the logical deduction required to uncover the truth.

This work is widely regarded as a quintessential entry in the historical mystery genre, praised for its meticulous period detail and the grounded nature of its protagonist. Readers often highlight the balance between the theological concerns of the medieval setting and the pragmatic, human-centric approach Cadfael takes toward solving crimes. The narrative style is noted for its steady, deliberate pace that mirrors the quiet life of the abbey while maintaining tension through the unfolding investigation. It remains a staple for those interested in character-focused mysteries that prioritize historical authenticity over sensationalism.