Cora Harrison 
Eye of the Law [EPUB ebook] 

A Mystery of Medieval Ireland
1510. A great feast is being held. Into a crowd listening to the story of Balor, the one-eyed god, come two strangers. The younger of the two, Larla, bears a letter that claims that the wealthy Ardal O’Lochlainn is his true father, which Ardal vociferously denies. So when Larla is found dead, with one eye missing, some think he was killed by the god, but most suspect Ardal. Mara, the Brehon of the Burren, is called to investigate.