This book kept me up all night listening. While seemingly a story of gratuitous murder, River of Darkness also explores the theme of how a person's psyche long after a war is over. War, in fact, is never over for some. Airth skillfully weaves together a police investigation, a love story, and a killer's narrative. I highly recommend this book. The narrator was excellent and his regional accents sounded authentic, at least to my untrained ear.
I enjoyed this book much more than I expected to. The author is very skilled at weaving the history and culture of the period into the story without inserting long lectures that stop the movement of the story. I liked the main character, Matthew Shardlake, even with his flaws and religious zeal. I hope Brother Guy turns up in a later book, though I agree he sounded Russian rather than Moorish. (I have found the same thing with other narrators trying to do a Middle Eastern accent.)
I considered giving the book a 5 but it could have done with one less murder. And Shardlake did seem to flounder, accusing almost everyone of murder at some point in the story. There weren't many options left by the end.