Books in the Merlin Mystery series

When Sir Agravain leads a dozen knights to arrest Lancelot in the queen's chamber, he kills them all in his own defense-all except the villainous Mordred, who pushes the king to make war on the escaped Lancelot, and to burn the queen for treason. On the morning of the queen's execution, Lancelot leads an army of his supporters to scatter King Arthur's knights and rescue Guinevere from the flames, leaving several of Arthur's knights dead in their wake, including Sir Gawain's favorite brother Gareth. Gawain, chief of what is left of the Round Table knights, insists that the king besiege Lancelot and Guinevere at the castle of Joyous Gard, goading Lancelot to come and fight him in single combat.However, Merlin, examining the bodies on the battlefield, realizes that Gareth and three other knights were killed not by Lancelot's mounted army but by someone on the ground who attacked them from behind during the melee. Once again it is up to Merlin and Gildas to find the real killer of Sir Gareth before Arthur's reign is brought down completely by the warring knights, and by the machinations of Mordred, who has been left behind to rule in the king's stead.

When word comes to Camelot that Sir Tristram has died in Brittany of wounds suffered in a skirmish, and that his longtime mistress, La Belle Isolde, Queen of Cornwall, has subsequently died herself of a broken heart, Queen Guinevere and her trusted lady Rosemounde immediately suspect that there is more to the story of the lovers' deaths than they are being told. It is up to Merlin and his faithful assistant, Gildas of Cornwall, to find the truth behind the myths and half-truths surrounding these untimely deaths. They take ship to Brittany to investigate, and find themselves stymied by the uncooperative attitudes of Tristram's close friend Kaherdin, lord of the city; his sister and Tristram's wife Isolde of the White Hands; and Brangwen, La Belle Isolde's faithful lady-in-waiting.The case is complicated by the facts that King Mark of Cornwall is Gildas's own liege lord, and that Duke Hoel, Lord of Brittany, is King Arthur's close ally and father of the lady Rosemounde, who urges Gildas to clear the name of her half-sister, Isolde of the White hands, whom gossip has implicated in Tristram's untimely death. By the time they are finally able to uncover the truth, Gildas and Merlin have lost one companion and are in danger of losing their own lives.