It's a day like any other day in a provincial city in central Russia. A 12-year-old girl is getting ready to go to school. Suddenly her phone rings. The next minute she is out of the door, saying she's meeting a friend and they will go to school together. Later the same day, when her mother turns up at the school, there is no sign of her daughter. No-one has seen her. This is really sad and terrifying.