In the summer of 1139, there is a pause in the civil war racking the country. St. Peter's Fair attracts merchants from across England and beyond, promising to bring some much-needed gaiety to Shrewsbury - that is, until the dead body of a wealthy merchant is found in the river Severn. Brother Cadfael offers to help the merchant's lovely niece uncover the murderer, but as he searches for the killer, the merchant's wares are ransacked, and two more men are murdered. Brother Cadfael suspects the girl almost certainly knows more than she is telling, and he desperately races to save her, knowing that betrayal can come from any direction - and even good intentions can kill.