‘The big problem for us was that we didn’t have CCTV,’ said the DI, warming to his theme of the guilty going unpunished. ‘You know the Met solves nearly one hundred murders every year with CCTV images? There are six million CCTV cameras in this country – one for every ten people – but not enough to stop every villain.’

Below me I could see Jackson walking towards Smithfield. But he did not go inside. He turned right and began walking towards Holborn Circus.

‘And there’s no CCTV cameras in toilets,’ I said. ‘Although they have them everywhere else, don’t they?’

‘I’m not allowed to disclose an image of a patient without their written consent,’ said the security officer at the Whittington Hospital.

‘I’m not looking for an image of a patient,’ I said. ‘I want to know who visited him.’

We were in the hospital’s security bunker. It was a darkened room with no natural light where four large screens each showed a grid revealing nine CCTV images, everything from the car park to the maternity ward, the A&E department to the main foyer.

‘How far can you go back?’ I said.

‘I can go back a month,’ the security officer said. ‘That’s how long we store the images.’ The grid of images was constantly changing on the large screens. ‘We’ve got one hundred and fifty cameras – pretty standard for a hospital like the Whittington – and when bad things happen, like a sexual assault on a mixed ward, or a baby abduction on the maternity ward, or the assaults on our staff that happen every drunken weekend of the year – they usually get reported immediately. What we looking for?’

‘Do you have images from the Critical Care Unit?’

He hit some buttons.

‘Waiting room, nurses’ station, entrance to the CCU – you need a card to get beyond the door. Nobody just wanders in.’

‘Let’s have a look at the nurses’ station.’ I thought about it. ‘Let’s start with weekend nights.’

The security officer went back to a Saturday night at the start of the month and found what I was looking for almost immediately.

‘Stop it there,’ I said.

Jackson Rose was on the CCTV.

He was holding a bouquet of flowers and smiling at a pretty Filipina nurse as if the flowers might possibly be for her as he walked past the nurses’ station on his way to visit an old soldier in a coma.

*  *  *

You see London’s homeless at night.

In the day they are invisible, or at least hard to tell from the people with homes. But at night they are revealed and there are places – pathetically few in a wealthy city of ten million souls – where they go to be fed.

One of those places is Waterloo. Under the arches where trains roar above your head, arches that are black with the fumes of today and the fog of long ago.