'Saint Peter's Fair' by Ellis Peters.
This is the first book in the second Cadfael omnibus. (The other 2 books are --- 'The Leper of Saint Giles' and 'The Virgin in the Ice.')
The year is 1139 and the date 30th July. This is an important day in the calender for the people of Shrewsbury for this is the preparation day , the eve of the festival of Saint Peter ad Vincula. He being one of the patron saints of the nearby abbey.
Following on from this festival is the fair for all the folks of Shrewsbury and merchants from afar. At this there is selling and buying of goods and the people generally enjoy themselves with much drinking and joviality.
Certain amount of money from the fair is given to the townspeople , via the abbey for the upkeep of the town walls and tracks , this they find insufficient and are most distressed when the Abbot refuses to suppliment their needs. So the seemingly happy fair is not starting in a very convivial way.
Now as all fairs proceed, some men are only around to cause trouble and these quarrels are usually between merchants from different areas. When one merchant is involved in a riot and then appears missing his only relative at hand a young neice is forced to employ the skillful ways of Cadfael in the hope of finding him. When the uncle is eventually found floating in the river and then another murder is committed Cadfael feels that the Fair is in chaos and as he persues the suspects prays that the Fair will have a peaceful ending, both for Abbey and townsfolk.
A very good read as all 'Cadfaels' are in my opinion.