As the car turned on to the hospital approach road, Holland said, ‘I still think we’re ahead of the game.’ It was the continuation of a conversation they had begun in the queue for a taxi, which had itself sprung from a discussion that had started just as the train was pulling into Cambridge station.

‘The game being?’

‘Catching him.’

‘Got it,’ Thorne said. ‘So, not knowing who he is, where he is or why the hell he’s doing this puts us ahead, does it?’

‘We do know who the other victims are going to be, though. That’s a decent result, surely?’

‘Half decent.’

The cab was crawling over speed bumps towards the hospital’s main entrance and Holland began digging into his wallet for cash to pay the driver. ‘At the very least we can make sure there aren’t any more killings.’

‘If we can find them,’ Thorne said. ‘I mean, it’s not looking too clever so far, is it?’

They had quickly established that there were four more likely candidates: the children of those victims of Raymond Garvey whose offspring had not already been successfully targeted. As of that morning, the team had only been able to track down and talk to one out of the four, and had only been able to trace her that quickly because of a criminal record.

‘One out of four?’ Thorne had been as angry as he was incredulous. ‘That’s piss-poor, Russell. We need to find the other three, fast.’

‘You think so?’ Brigstocke’s tone had been every bit as sharp as Thorne’s. ‘Maybe you should be sitting on this side of the desk.’

‘I’m just saying, we need to concentrate on finding them, getting them into protective custody or whatever.’

‘Nobody’s arguing.’

‘That needs to be our top priority.’

‘I’m well aware of that, Tom, which is why I’ve got everyone except the cleaner working on it.’

Thorne had stood in the doorway of Brigstocke’s office and nodded, suddenly aware that he might have been coming across as a little self-righteous. ‘It wasn’t a criticism-’

‘So, why don’t you stop going on like you’re the only one who gives a shit and get out there and do your job?’

The cab stopped and Holland passed the money forward, gave a reasonable tip and asked for a receipt. The driver kept one eye on the rear-view mirror as he scribbled. He had clearly been ear-wigging all the way from the station, and when he had torn off the slip of paper and handed it across, he asked Holland if he and his friend were there to arrest anyone.

Thorne climbed out and slammed the door.

‘Got anybody in mind?’ Holland asked, one foot already outside the car.

The driver grinned. ‘I could tell you some bloody stories and that’s the truth.’

Holland slammed his own door then and followed Thorne, caught up with him by a small cluster of smokers gathered outside the entrance. ‘Is your glass ever half full?’ he asked.

They strolled through the automatic doors, walked past a small shop selling magazines and chocolates, soft toys and bunches of flowers that made the average garage look like a Kensington florist’s. ‘You think I should look on the bright side a bit more?’

‘Just admitting that there is one might be a start,’ Holland said.

Once they had passed through the A and E Department’s reception area, they stopped to ask directions. Eventually they picked up signs for the Neurological Department and a few minutes later were walking towards the lifts that would take them up to the right floor.

‘You got any mints or anything?’ Thorne asked.

Holland shook his head. ‘We could nip back to that shop.’

Thorne said it didn’t matter. He was not a big fan of the smell, that was all. Bleach and whatever else. He had glanced up at the signs as they’d walked.

Oncology. Dementia Unit. Antenatal Suite.

‘It’s a bloody stupid expression anyway,’ he said. He tried to keep his voice level. ‘Surely what’s in your glass is a bit more important.’

‘I suppose.’

‘What if it’s a dirty glass and it’s half full of hot piss?’

They finally found the room they were looking for behind a busy ward, at the far end of a corridor with a shiny grey floor and paintings on the wall that looked as though they had been done by patients still recovering from head injuries. The sign on the door said ‘Neurosurgical Secretaries’ and, on entering, Thorne and Holland were confronted by three women who turned in unison and stared. Holland let them know, in a quieter voice than Thorne was used to, that they had an appointment. The eldest of the women stood up and walked past him to a door that was all but hidden by an enormous filing cabinet. She knocked, and after a few seconds’ muttered conversation, Thorne and Holland were shown into Doctor Pavesh Kambar’s office.

Thorne nodded back towards the secretaries’ room. ‘They all yours?’ he asked.

‘I share them,’ Kambar said. He spoke like a newsreader on Radio 4. ‘There’s something of a pecking order.’

‘Are you talking about the doctors or the secretaries?’

‘Both.’ Kambar nodded the same way that Thorne had. ‘But it’s rather more fierce out there.’

Kambar was a fit-looking man in his mid-fifties. His hair was thick, silvering, like his well-trimmed moustache, and the dark suit and polished brogues, though understated, were clearly expensive. By contrast, his office was windowless, no more than a quarter the size of the one shared by the secretaries, and there was only one chair other than his own. Thorne took it, leaving Holland to lean back a little awkwardly against the door. A year planner was mounted on the wall, while Holland ’s head rested at the same level as a model of the human brain that sat at the end of a bookshelf, its different sections moulded in brightly coloured plastic: blue, white and pink.

Thorne turned and looked from Holland to the model. ‘It’s probably a damn sight bigger than yours,’ he said.

While Thorne told Kambar about their journey up, and the doctor bemoaned the vicissitudes of the London to Cambridge rail service, Holland dug into his briefcase for a photocopy of the pieced-together X-ray fragments. He handed it over. ‘What we talked about on the phone.’

Kambar nodded, studied the picture for a few seconds. He turned to his computer and punched at the keyboard. ‘And this is where it comes from…’

Thorne shifted his chair a little closer and peered at the screen. There were three images which, at first glance, appeared identical: a cross-section of a brain, grey against a black background, with a white, almost perfectly round mass towards the bottom.

‘I printed one out for you,’ Kambar said. He opened a drawer and took out what looked like a large X-ray. ‘These days all the images are digital, stored on disc, but we still occasionally use film if we need to.’ He fastened the X-ray to the light box that ran the length of the wall above his desk and studied it, as though he had never seen it before.

‘So what happened to the original?’ Thorne asked.

‘There was no original as such,’ Kambar said. ‘As I explained, the scans are stored on computer.’

Thorne pointed to the photocopy lying on Kambar’s desk. ‘So where did they come from?’

‘Well, nobody would have had any reason to print one of these things out before I did,’ Kambar said. ‘So, my guess is that they’re from one of the series I printed out and gave to Raymond Garvey a few weeks before he died. Every patient is fully entitled to keep copies of all their medical records.’ He pointed as Thorne stared at the images. ‘The white mass is the tumour, obviously.’

Holland had moved forward. ‘Looks enormous,’ he said.

Kambar made a fist. ‘That big.’

‘How long did you treat him?’ Thorne asked.

Kambar fiddled with a pencil as he took them through a potted history of Garvey’s diagnosis, treatment and, ultimately, his death. Holland made notes and Thorne listened, his eyes drifting occasionally to the pictures, stark against the light box. The simple white shadow, round and smooth, looked like nothing.