Mystical detective novel for children and teenagers. The main characters - brother and sister - investigate the mystery of their new neighbor and the disaster that happened 100 years ago. Since his father left the family, Cooper began to distance himself from his friends, constantly quarrel with his younger sister Jess and be angry with his new neighbor. which suddenly appeared in a house that had recently been abandoned. Meanwhile, Jess began to study a fatal train accident that occurred a hundred years ago, in which one boy could not be identified. His distinctive sign was a strange emblem on his jacket - a symbol that no one had seen either before or after the disaster. By a mysterious and frightening coincidence, it turned out that the new neighbor had the same sign on her clothes. Cooper and Jess, plunging deeper and deeper into the history of a hundred years ago, begin to realize that their city is in serious danger. Published in Russian for the first time.