The Devil's Novice
by Ellis Peters. This is the eighth of the Brother Cadfael mystery series and another good read.
A local young man decides to take vows in the abbey, and another man, an emissary of the bishop, goes missing at roughly the same time. The new novice has terrible nightmares and brother Cadfael suspects there may be a connection between the novice's entry into the abbey and the missing man. Family strife and political intrigue surface when the bishop's emissary turns up dead, and brother Cadfael unravels the chain of events.