Two years later, and shortly after the story has been revived in a Sunday Times feature about missing girls, the investigating officer, Inspector Ainley, is killed in a road accident.

She had gone home for lunch, and was apparently last seen by a lollipop man, wearing her distinctive uniform and carrying a bag, on her return journey to school.

These include Valerie's mother, Grace Taylor, who bears a close resemblance to her daughter, and stepfather, George Taylor, a worker at the city rubbish tip; the school headmaster, Donald Phillipson, and his wife Sheila, between whom there is an element of mistrust; Reginald Baines, second master and previously an unsuccessful candidate for the headmastership; David Acum, a French teacher who had taught Valerie's last lesson, but who left Oxford not long afterwards to teach in Caernarfon, North Wales; and Johnny Maguire, a former schoolmate of Valerie, now working at a strip club in London.

The clinic refuses to divulge further information, but Morse interviews Yvonne Baker, a girl who had shared a room with her there, and who vaguely remembers Valerie saying that the father of her child was a French teacher.

He has theorised that the woman posing as Mrs Acum may in fact be Valerie Taylor; but her fluency in French and other clues now persuade him that he is mistaken.

Acum admits that he had had a sexual fling with Valerie, was probably responsible for her pregnancy, and helped pay for the abortion, but says that he knows nothing about what happened to her subsequently.

Sheila Phillipson gained some knowledge of this, and, for the sake of her marriage, had gone to confront Baines: she now signs a confession admitting killing him – but Morse is convinced that she is lying, and perhaps covering up for her husband.