Tallinn (formerly Reval) in the year 1409: A high-ranking order knight, traveling from Visby to Marienburg, is brutally murdered on the Cathedral Hill. Everything suggests that the murderer has fled from the Cathedral Hill into the city, as further murders throw the town into turmoil. City apothecary Melchior Wakenstede, along with the court bailiff Wentzel Dorn, seeks to solve the series of murders. In his search for the killer, he encounters a variety of people and their possible motives: at festive gatherings in the Guild of the Blackheads, in magnificent merchant houses, in the Dominican monastery, and in dubious taverns outside the city walls. The Gothic St. Olaf's Church, with its ancient, mystical legends, plays a central role in the events, being one of the tallest towers in the world at that time. Just as the apothecary seems to be getting a little closer to the solution.