1354, numerous rumors circulate throughout Spain about the Holy Grail, a sacred cup that is supposedly hidden somewhere in the Pyrenees. Meanwhile, in Girona, a traveling merchant named Baptista is trying to sell a certain silver cup. However, the deal did not go through: someone killed the buyer and took the money. The townspeople are confused, believing that the sacred cup is now in Girona and the power of the Holy Grail will destroy them all. The blind doctor Isaac understands that the cup the merchant was selling is an ordinary one. But when an unknown killer deals with the merchant, Isaac begins his own investigation. “The Sinner’s Tranquilizer” is a continuation of the fascinating series of historical detective stories by Caroline Rowe (the pseudonym of the historian and writer Medora Sale) about the investigations of the blind doctor Isaac from Girona.