This book doesn't come up in a title search, even if you combine a keyword from the title and the author's name. I had to search for it by ISBN #. [2015--this seems to have been corrected]
Up until the middle of this book in the series, the Sheriff of Shropshire is Gilbert Prestcote. He's not particularly adequate. He's dour, he's prejudiced, and he sometimes takes advantage of built-in cruelties in the law to 'solve' problems that could have been solved a lot less ruthlessly. Would a man who accidentally killed another in a drunken (and fair) fight be convicted of murder in our society? It's less than likely. And he wouldn't have been convicted in Wales, either, at the time. He'd have been fined severely; he or his family would have to pay 'galanas'. But he wouldn't have been killed himself.
But it's not just the enemies Prestcote has acquired along the way (some of them reaching back for generations) that have made him an unsatisfactory Sheriff. Often, in earlier books, people feel pressured to solve cases in haste before Prestcote gets back from wherever he's off to this time, because experience shows Prestcote will just take whoever's nearest, and not worry about niggling details.
The position of Sheriff is not an elected one at this time. If it were, most people would have voted for the Deputy Sheriff, Hugh Beringar of Maesbury, who's a lot more careful to find the right suspect. But even he often has to turn a blind eye to achieve the spirit rather than the letter of the law.
In this book things change. In the previous book (The Devil's Novice), a battle against the Earl of Lincoln becomes imperative, if England is going to stay unified. The abbey doesn't want any battles at all, and they meet to pray for better counsel. But there's not much hope of it. So by early February, 1141, the war party are off to attack Lincoln (and his ally and brother, Chester).
And the battle is a disaster. Not just for King Stephen's side. The Northerners also suffer (the citizens of Lincoln, for example, are abused for backing Stephen against the Earl). And the capture of King Stephen is a major blow for his own side, but it doesn't necessarily improve Empress Maud's position, either. People are still reluctant to support her, at least partly because she's so intolerant of halfhearted support.
In Shropshire, however, the locals are more concerned about the injury and capture of Gilbert Prestcote. Since he was in the part of the battlefield that was overrun by the Welsh of Powys under Cadwaladr (brother, but no very obedient brother, to Owain Gwynedd), there's hope he may be ransomed. But in trade for whom?
Enter Avice of Thornberry (the longtime mistress of a nobleman from The Leper of St Giles), to the rescue once again. Now renamed Sister Magdalen (why should she deprive her innocent sisters of the notion they're rescuing her from infamy?), she explains how she and the foresters repulsed an attack by a band of Welshmen from Powys. And have they got a prisoner worthy of exchange? You bet they have! Elis ap Cynan makes his entrance tied up on horseback, favoring one cheek in the saddle, and cursing his captors in Welsh, in such an even voice that those who don't speak Welsh don't take offense.
A royal relative is surely adequate ransom for a Sheriff, so negotiations begin. The process is complicated by many things, one of which is NOT the reluctance of Owain Gwynedd to improve relations with Shropshire. Owain Gwynedd is heartily praised in this whole series, as an intelligent, wise, and foresighted man.
But there are other problems, involving fosterage and its relationships, child betrothal, and the fact that Elis is a sucker for a tall, pale girl with spun-sugar hair...who happens to be Gilbert Prestcote's daughter. Elis, the eternal optimist, thinks these problems can be easily solved. Melicent isn't so sure.
All in all, there are a lot of wrung hearts when the badly injured Lord Prestcote is escorted home by courteous Welshmen. And the matter is not eased when Prestcote dies, and it's proven to be murder. And all along, there are the Welsh of Powys, still out for loot, and still smarting for their defeat at Godric's Ford...
The rescue of the cattleman Anion, who aspires to his proper status as his father's son in Wales, is another complication. I don't think it's much of a spoiler to say that it's happily resolved, since he wasn't much of a suspect to begin with. Even other suspects point out that one of the reasons he fled into Wales was that, being without powerful supporters in Shropshire, he couldn't get a fair hearing there, and fled for fear he should prove the convenient nearest.