Monk's Hood by Ellis Peters

The year is 1138 and England is in the midst of civil war between King Stephen and the Empress Maud. But for now, the town of Shrewsbury has been left in an uneasy peace with both monarchs gathering their forces elsewhere.

Even so, plots are afoot within the Abbey town. Gervase Bonel, a wealthy landowner has bequeathed his land to the church and plans to live out his days in the sparse comfort of the abbey. So, when the man falls ill, it is the abbey’s herbalist and sometime detective Brother Cadfael who hurries to his aid. Cadfael is unprepared for what he finds for not only has Bonel been poisoned with monk’s hood oil but someone has used Cadfael’s own supply!

Confusion amounts over who was the intended victim as Bonel’s poisoned meat came from the Prior Richard’s own table, and even Cadfael himself is suspected for not only did the poison come from his laboratory, but the victim’s wife, Richaldis, was once Cadfael’s betrothed.

The obvious suspect is Bonel’s stepson, who has reason enough to commit the murder, but Cadfael is not convinced of the boy’s guilt and sets out to learn the truth of this deadly mystery.

Not into books? Then don’t miss the excellent TV series, starring Derek Jacobi as Brother Cadfael!