My copy of THE KING ARTHUR COMPENDIUM is in storage, but I'm fairly sure that the Chaosium edition is a reprint of a book that wasn't originally a game tie-in (that said, I think I bought my copy, a hardcover, from a games shop). Karr also wrote an excellent Arthurian mystery novel, THE IDYLLS OF THE QUEEN, in which Sir Kay sets out to clear Guenevere of a murder charge, relying on detective work rather than trial by combat.