Dead Man's Ransom (Cadfael #9)

Dead Man's Ransom (Cadfael #9) - Ellis Peters Set in the 12th century, The sheriff of Shrewsbury is captured by the Welsh, and a minor Welsh lord is also captured by the English. A swap is agreed, but one is murdered before the handover can take place.
Brother Cadfael uses his knowledge to pick at clues until the killer can be found.

A character driven story, it doesn't go in for convolutions that some mystery authors chose to show off how clever they were, and as such has much more re-reading value.

The period it's set in acts as a handy backdrop for the events that take place, and Peters has a good way with people's language and the way they talk.