The Leper Of St. Giles, by Ellis Peters
The fifth book  of the Cadfael Chronicles, this one deals with a complicated murder involving a mean-tempered old man with a long-term mistress and a squire in love with the very young lady (old enough to be his granddaughter) who has been coerced into the wedding by her uncle and guardian. While this mystery is being solved with an obvious suspect (namely, the squire) being not guilty but looking guilty. I am impressed at just how often this series points out that people tend not to investigate the truth when someone obviously looks guilty and has an easily conceivable motive, and how rare someone is who is willing to give the benefit of the doubt and dig deeper. Here too Cadfael’s experience in the Crusades and his wide experience in dealing with people allows him to recognize honest people as opposed to those who are playing a much more dangerous game.
In this case, parts of the mystery are not difficult to solve at all. A young man bonds with his future grandfather-in-law while they are both seeking the interests of a beautiful heiress, and there is little to help bond people together than shared projects where both parties can show their character and become allies with a common cause, even if the law is against them. Here too there is a concern for class–the young woman is supposed to marry a young man, not an old man, and the young man happens to be their heir to some manors of himself and therefore a member of her class, and a man with a sense of fair play as well, and so a suitable partner to protect the estates of a young woman whose manors served to enrich a greedy uncle rather than serve her own happiness. So too we see a mistress, cast off when her partner dies, faced with no good option but to seek retirement in a nunnery because no other honorable options exist for a Norman’s whore whose family cut her off, and who is too old and too dishonored to be seen as anyone’s wife.
The theme of honor runs heavy in this novel, giving it a depth far beyond its plot. A young orphan seeks to honor her guardians even as they take advantage of her. A boy honors his mother even as she dies of leprosy. A family dishonors a clear-eyed and honest relative who saw a chance at a better life, even if it was an immoral one. A young man honors an old leper who turns out to be far more important than (almost) anyone could have guessed, even if he is dishonored by many who consider themselves to be important. The abbot goes out of his way to honor the magnates who come to celebrate a marriage in Shrewsbury, only to end up honoring them by providing them burial after their demises, and Cadfael, as is his noble fashion, honors those he meets, no matter how old or young, no matter their socioeconomic status or gender, seeking truth and a great deal of justice and mercy, and finding more of it than any of us have a right to expect.
 See, for example: