A teacher is killed at a prestigious gymnasium. At the same time, a notebook was stolen, where she wrote down all the sins of the schoolchildren, as well as several personal items, including a gold ring with a natural ruby. The murdered woman, known for her bad character, spoiled the blood of many: students, their parents, colleagues. A variety of people come under suspicion. But Arkady Kazik, a professional psychologist and just a fan of prying into other people’s affairs, will sort all this out together with the police. The novel will delight all fans of the classic detective story.