Eight murders shocked the small town. A mysterious maniac, dubbed the Cleaner by the press, marks the bodies of his victims with the sign “infinity.” On what basis does he kill? What is the meaning of his “messages”? The investigation is led by two brilliant intellectuals - journalist Stephanie Delacour and Commissioner Northrop Rilski. Gradually they come to a shocking conclusion: the bloody deeds of the Purifier are somehow connected with one of the most mysterious periods of world history - the fall of Constantinople under the onslaught of participants in the First Crusade. The key to the mystery what is happening should be sought on the pages of the famous chronicle written by the Byzantine princess Anna Komnena...