Brother Cadfael's Penance
by Ellis Peters. This is the twentieth, and last (regrettably) installment of the Brother Cadfael mystery series. The author, whose real name is Edith Pargeter, died peacefully just after this installment went to print in the paperback Mysterious Press edition.
Cadfael gets information that his son has been taken prisoner in the ongoing civil war between King Steven and the Empress Maud (called the Anarchy by historians) and held without bail or possibility of parole. He gets permission from the abbot to attend a peace conference to find information, but not permission to go any further. Cadfael becomes an apostate to find his son with no guarantee of a welcome back to his monastic life afterwards.
This was a really good story and in fact one of the best of the books. The author gives a detailed account of a medieval siege and battle. There are themes of reconciliation and father-son dynamics that are really well done.
I will have to re-read this whole series of twenty books. Brother Cadfael and the supporting characters of this series are unforgettable.