The Unlikely Spy. The Gareth & Gwen Medieval Mysteries, #5

Murder and music lead to mayhem in medieval Wales in the fifth Gareth & Gwen Medieval Mystery . August 1146. Prince Hywel has called all the bards of Wales to him for a music festival to mark the third anniversary of his rule over Ceredigion. He has invited all the lords of Wales too, including his father, his uncle, and his neighbor to the south, King Cadell. But with the highborn also come the low: thieves, spies, and other hangers-on.
And when a murderer strikes as the festival starts, Gareth and Gwen are charged with discovering his identity-before the death of a peasant shakes the throne of a king. The Unlikely Spy is the fifth Gareth and Gwen Medieval Mystery. Complete Series reading order: The Good Knight, The Uninvited Guest, The Fourth Horseman, The Fallen Princess, The Unlikely Spy, The Lost Brother, The Renegade Merchant, The Unexpected Ally, The Worthy Soldier, The Favored Son, The Viking Prince, The Irish Bride, the Prince's Man, The Faithless Fool, The Honorable Traitor, The Admirable Physician, The Shattered King.
Also The Bard's Daughter (prequel novella).