Patrick had personally scoured the CCTV footage from the car park. One camera had caught the briefest glimpse of a man in a dark jacket carrying a child who looked like Liam, but it was impossible to see the man’s face or where he’d gone. Zoe insisted that the man who’d bumped her had been wearing a black jacket, but she had barely looked at his face, the photo-fit they’d put together from her patchy memory likely to be 90 per cent imagination. This hadn’t stopped the picture from being printed on the front of every newspaper in the country, sparking hundreds of calls from members of the public saying the man looked like their neighbour, their boss, their husband. Every single one of these unfortunate men had been eliminated from the investigation.

Patrick wouldn’t say the last week had been the hardest of his life – he’d had much darker weeks – but they had been long, frustrating and exhausting. Huge pictures of Isabel and Liam hung in the incident room. Their images were burnt into the retinas of every man and woman on the team. But so far, though Patrick would never admit this in public, they hadn’t got a bloody clue what had happened to the two kids or where they were.

It was as if they had evaporated.

A red light caught them and Patrick saw another phantom infant flash before his eyes, running between the stopped cars. His whole body thrummed with the need for sleep.

‘When you were younger,’ he said, ‘did you ever think you’d be spending your evenings locked in a room with a paedophile with a comb-over and halitosis?’

‘Oh god, don’t remind me. It’s in my nostrils. What causes that smell?’

‘Rotting gums. They should send him round schools as a warning to children about cleaning . . . Or maybe not – what the fuck am I saying?’

The interview had been a waste of time. Chris Davis was sixty now and had served his time for the abduction of a little girl thirty years before. But as he lived only a few streets away from Isabel Hartley and her family, he was on the list. But he hadn’t done it. He had an alibi for the disappearances of both Izzy and Liam.

It had been almost a week since Isabel had vanished, and five days since Liam. The chances of finding them diminished with every passing day – no, every hour.

‘What do you think they should do to people like Davis?’ Carmella asked. ‘Chemical castration? String ’em up? You should hear me ma, the things she says about child murderers. Like Baby P – she was on one of those Facebook groups calling for his stepdad to have his balls ripped off in front of a baying crowd, and salt rubbed into his bleeding, empty . . .’

He winced. ‘Carmella! Please!’