They talked through the possibilities, agreeing that nothing could be done until a complaint had been made. He changed the subject to something less gloomy while they finished the wine, a fresh pinot grigio, and rounded the evening off with a fiery shot of grappa. The walk home was a delight; they cut across a darkened park away from the main road, and had a slightly drunken kiss and cuddle by the swings, just as if they were teenagers. For a dare they clambered over the wooden palings which marked the park’s northern boundary, earning themselves a tut of disgust from a late-night female dog walker. Gillard carried his giggling wife over his shoulder the last 200 yards into the cul-de-sac, and with mock shushing and whispers tiptoed past his aunt’s bungalow. Still holding Sam, this time like a battering ram, he ran across the street towards their front door, and pretended to bash it in with her head, yelling: ‘Armed police!’

After numerous attempts to insert the key one-handed, Gillard opened the door, and toppled with Sam onto the doormat. Both laughing uncontrollably, they wriggled around, until he could kick the door closed behind them. The laughter suddenly ceased, the couple staring into each other’s eyes, the kissing became passionate, and he said: ‘Look, the Surrey bodice ripper strikes again!’ He attempted to tear off her pullover, but Sam became entangled in the sleeves. She made short work of his suit and tie, and when they made love, passionately, it was on a pile of flyers offering pizza and curry delivered to your door.

Tuesday

Sitting with his head in his hands at his desk, DCI Craig Gillard contemplated the impasse he was at. What on earth had happened to Beatrice Ulbricht? All of the usual electronic and technical tools available to CID – CCTV, mobile phone cell site analysis, and finally ANPR – had so far either drawn a blank or simply created contradictory ideas. They couldn’t find a single vehicle that had been both in Earlsfield and within the vicinity of Clandon station on that Tuesday afternoon, not even the van of the man who had seen Beatrice at the bus stop.

The breathless arrival of Detective Inspector John Perry broke into his reverie. ‘Craig, you are not going to believe this.’ He was waving his smartphone around excitedly.

‘Try me.’

‘The girl under the bridge has a DNA match on the national database, with a missing person called Jane Morris.’ Perry turned back to the phone, as if reading it properly for the first time. ‘It’s a cold case last reinvestigated by the Met in 2006.’

‘Let’s have a look,’ Gillard said. Perry passed him the phone, and he scrolled down the text. ‘This can’t be right, John. The girl in the river could only just have been born in 2006. Did she disappear as a baby?’ Gillard scrolled down to the date of the original investigation. ‘No, Jane Morris disappeared in 1982, aged fifteen. Is that just a familial DNA test?’