Math textbook for the 5th grade. According to the terms of the task, every day a Pedestrian goes from point "A" to point "B", along the way he meets a Cyclist. Then he returns home, where his faithful wife is waiting for him. The next day, everything repeats. But one day the Pedestrian is stopped by an Investigator and informed that the Cyclist has disappeared. The investigator asks the Pedestrian to go with him to point "B" to interview witnesses and figure out this confusing story together.