In the autumn of 1271, when an autumn storm raged on the east coast of England, a crusader was found slaughtered near the Tyndale monastery. On the dagger sticking out of the body, strange writing was visible, similar to Arabic script... What is this - the revenge of the mysterious and ruthless eastern sect of Assassins? Or did the killer really want people to think so? Local coroner Ralph undertakes to solve the crime and find the villain, but the case turns out to be even more complicated than it seemed at first glance. Ralph's involuntary assistant becomes the doctor Brother Thomas, who arrived at the monastery on a secret mission, and the abbess Elinor. Each of them has their own hidden motives to find the real killer.