There’s no need for Strover to feel guilty too. It was his idea to push Kate into the spotlight. Silas waits for her to speak, but she’s not confident enough to openly criticise her boss.

‘It was a mistake,’ he reminds her. ‘My mistake.’

‘The OCG would have found Kate eventually, if they were committed to harming her,’ Strover says. ‘With or without publicity.’

‘You think so?’

Neither of them seems convinced.

‘I came across something else, too, when I was searching to see if any other super recognisers had given interviews,’ Strover continues.

‘The Met unit did – told anyone who would listen about their success at the London riots,’ Silas says.

One poxy criminal was identified by recognition software in the aftermath of the 2011 disturbances, even though the Met had gathered 200,000 hours of CCTV footage. When the footage was passed over to the spotters, a single super recogniser made 190 IDs. Interestingly, the Met gave no interviews when the unit identified the two Russian GRU officers who had travelled to Salisbury to poison Sergei Skripal with the nerve agent novichok.

‘And the Australians,’ says Strover. ‘And the Germans. They’ve all been talking about their successes.’

‘You were busy last night.’

‘Couldn’t sleep.’

Strover retrieves a sheet of paper from her jacket pocket. A printout of an article.

‘Not sure it’s relevant now, but I thought you might want to see this,’ she says.

Silas takes it and starts to read. The article is about an Irish super-recogniser unit that was set up in Dublin at the same time as Wiltshire’s. But it’s the photo staring back at him that has his attention.

‘She’s still missing,’ Strover says, but Silas is not listening. ‘Their star recogniser, two years younger than Kate. Disappeared a month ago.’

Silas tears through the words. The female officer vanished late one night on her drive back from work. As with Kate, she possessed exceptional powers of facial recognition and was responsible for the arrest of a number of petty criminals. Nothing major, apart from one suspect who was caught after she’d spotted him at a football match at the Aviva Stadium in Dublin. He was subsequently charged with murder.

‘You need to widen your search,’ Silas says, a new urgency in his voice. ‘See if any other super recognisers have disappeared. Dublin’s not alone.’

He tells her about the call last night from the detective in Nottingham. She’s shocked, but her eyes light up. Two small dots have been joined. It’s the bit of his job that Silas likes the most, watching the bigger picture emerge.

‘Search the UK first, then Europe,’ he continues. ‘Check with Europol too – see if they’re aware of any missing recognisers.’