Paladin. The Welsh Guard Mysteries, #3

Catrin and Rhys travel to Windsor Castle for their third medieval mystery together.August 1284. On the heels of King Edward's triumph over Wales, the high point of his reign thus far, he receives the worst news possible: his eldest living son and heir to the throne of England has died. Concerned that his victories in Wales, and even more the means by which he came by them, have brought the wrath of the Almighty down upon his house, King Edward sends Catrin and Rhys to Windsor Castle to investigate.
But although they find victims and villains aplenty, their far greater test-of friendship, loyalty, and allegiance-is managing the expectations of a grieving king, who fears his son was murdered-and fears even more that he wasn't. Paladin is the third book in The Welsh Guard Mysteries. Series so far: Crouchback, Chevalier, Paladin, Herald, Bardd.