Ideally, read all the preceding books in the series, in order, before reading this one. At a minimum, first read #1 (_A Morbid Taste for Bones_, the story of how St. Winifred's reliquary came to the abbey) to avoid spoiling the end of that book, and _The Potter's Field_, which introduced the Blounts of Longner. If you're interested in an audio edition, check that you're getting the unabridged recording narrated by Stephen Thorne.
In the summer of 1144, Geoffrey de Mandeville - after more than a year of running the Fens as his own private robber kingdom - was shot almost by accident during a siege, and died from the infected wound. His lengthy death gave him no chance to receive absolution - only the Pope could have absolved one guilty of the seizure of the abbey of Ramsey - but Geoffrey's followers did what they could for him, restoring the despoiled abbey to its scattered monks. Thus the abbey of St. Peter and St. Paul receives two guests of their own order from Ramsey - grim subprior Herluin and his appealing assistant Tutilo - asking leave to preach. Ramsey needs money, materials, and labour to undo the damage left by Geoffrey's marauders.
Herluin guided their footsteps to Shrewsbury not only to request assistance, but to recall Sulien Blount of Longner, sometime novice of Ramsey, who was sent home to reconsider his vocation. (See _The Potter's Field_ for details.) Cadfael, therefore, accompanies Herluin and his young companion Tutilo to Longner to speak with Sulien - and appeal for the Blounts' generosity toward Ramsey. While Herluin pursues his errand, Cadfael introduces Tutilo to Sulien's dying mother, the formidable Donata, who is more than happy to welcome a bard, even if he's now a novice monk. (Their friendship, brief as it is, is touching.) Young Tutilo is what would now be called a renaissance man, and would be wasted as a monk - if he ever gets that far after meeting the Irish girl Daalny, slave to the Provencal troubadour staying at the abbey guesthouse. Daalny's voice is such as to attract any musician - part of the troubadour's stock in trade. Nevertheless, Tutilo seems passionate enough on Ramsey's behalf.
Unfortunately, someone appears to have been a little *too* enthusiastic for Ramsey's sake - while preparing for a flood, someone stole St. Winifred's relics, and the chief suspects are the brothers of Ramsey. How, after all, could anyone steal the reliquary if the saint didn't *want* to go elsewhere? To further complicate the ensuing dispute over the saint's wishes, the reliquary comes into the hands of Earl Robert "Bossu" Beaumont, a brilliant man with a sly sense of humor who decides to further complicate matters by pointing out that the saint came to rest in *his* care and seems content to stay there. (Robert - who was a real person, incidentally - here makes his debut in the series as a very impressive figure; the crooked back that gave him his nickname doesn't hinder him at all.) Only Brother Cadfael and his confidant Hugh Beringar know just how complicated this situation really is - before a man on the fringes of the quarrel is murdered on a dark night. But was he killed for himself - or because he was mistaken for one of the disputants?
Very nicely ties up some loose ends from _The Potter's Field_, while raking up the old problem of the reliquary very creatively. Robert Bossu alone would be worth the price of admission. :)