Brother Cadfael was the trend-setter that made publishers and authors aware that history and mystery could be combined to make good stories that sold well.  His books appeal to almost everyone - they are light, enjoyable reading that incorporate the medieval background in a way that adds interest but does not require previous knowledge on the part of the reader.  While the author gets her facts right about the period, the atmosphere can be a bit "cozy" - true love always wins out, endings are usually happy and few are the ailments that cannot be helped by Cadfael's herbal potions.

The stories take place within a 10 year span that was a period of tension and upheaval in England as civil war raged over whether Stephan or Mathilde would control the throne.  A few of the mysteries use this as a starting point, but many of the others take place in a quiet, reasonably peaceful Shrewsbury that is often infiltrated by spies or agents of both the combatants or troublemakers from Wales, whose border is quite close.  While each book is clearly placed in a particular year, Brother Cadfael and the circle of people with whom he interacts  offer a timeless continuity in a somewhat romanticized, but always interesting 12th century England.