Peter is a planning officer at Nottingham City Council. Every day, as he boards the bus for work, he notices a girl who gets on at the same stop and spends the journey scribbling furiously in a battered notebook. One day she doesn't get off at her usual stop, but dashes off to the railway station instead, leaving her notebook on the bus. Peter picks it up and starts to read. When the girl (Sophie) goes missing and the police are called in, Peter, having read her journal, knows more about her than anyone else. He also knows that the truth about what finally happened to Sophie is a truth he must keep entirely to himself.