The book introduces young readers to the life of students of one railway school. But this is not an ordinary school. This is a boarding school where children study and live. And only on Saturday they go home to spend Sunday with their relatives. "Crystal Key" is a book about the life and friendship of sixth-graders, about the Ural girl Ksyusha Cherdyntseva and her family, about teachers and pioneer leaders, about the events that took place in the sixth grade "b" during the school year.