The Lark's Lament — Alan Gordon

In 1204 A.D., the Fools' Guild is in hiding, under attack from the forces of Pope Innocent III. Theophilos and Claudia, jesters with the Guild, are sent to enlist the help of a former guild member - the minstrel Folquet, now the abbot Folq at a Cistercian monastery - to intercede with the pope on their behalf. But while they are at the abbey pleading their case, a gruesome murder takes place - a monk is killed in the librarium and a cryptic message written on the wall in his blood.
In the wake of the murder, Folq issues an ultimatum to Theophilos. If he learns the meaning of the message and finds the killer, Folq will help the Guild. But if the Jester fails, Folq will have the pope declare the Guild anathema. With the future of the Guild on the line, Theophilos, his wife, and their apprentice go off in search of Folquet's past and the meaning of the message, uncovering a long-ago series of events that were as deadly then as they are proving to be now.