The Puppet Show (Washington Poe)

It made sense. She was trying to find vehicles that had passed the cameras nearest to the killing sites and had also passed cameras near the likely abduction sites.

‘We have five victims,’ Flynn reminded her.

‘We do, DI Stephanie Flynn, but for analytical purposes the man in Quentin Carmichael’s coffin is an outlier. We don’t know when he was put in the coffin and we don’t know where or when he was killed.’

She paused to let them catch up. Poe noticed that when she was talking about data, she lost her awkwardness.

‘Of course, we’re not in London so ANPR cameras only cover the M6, the A-roads and some of the bigger B-roads, but I calculated that in all the abductions, some of these cameras would have to be crossed at least once: the ones on the M6 and the ones that cover the roads that cross the M6.’

Poe agreed. A bit like a major river, the M6 corridor bisected the county through the middle. It was inconceivable that the Immolation Man hadn’t had to cross the motorway at least once. In all probability he’d passed over it, under it and driven along it several times.

Bradshaw continued. ‘But the ANPR list was far too big. It was six figures high.’

‘People use their cars more in rural counties,’ Poe explained. ‘ANPR covers all the commuter routes so I’m surprised the number wasn’t bigger.’

‘After I’d run the numbers through my program, it became a bit more manageable. I split the list into three. The first list is the vehicles with the highest probability. Eight hundred and four in total,’ she said. ‘That’s the list I coloured in.’

As well as logging all necessary details like a vehicle’s registration, where and when it was snapped, that type of thing, ANPR cameras also take two photographs: one of the registration plate and one of the whole vehicle. When Bradshaw said she’d had some

of the ANPR data ‘coloured in’, she meant she’d downloaded those photographs. And probably to appease her analogue colleagues, she’d then printed them off.

The cost didn’t matter, though; Bradshaw had two PhDs, she was a member of the Mathematics Institute at Oxford University, and she had an IQ higher than anyone Poe had ever heard of. If she said the killer was in that pile of paper somewhere, then he believed her.

He settled down to read. Flynn did the same.

Bradshaw smiled.

ANPR was a fantastic investigative tool when you knew what you were looking for, but its big weakness was that when you were casting a net, it was virtually worthless. It caught everyone, and Poe knew this was why Gamble hadn’t really bothered before. He was sure that at some point he’d have tasked detectives with reviewing ANPR, but it would have been to tick boxes rather than a genuine investigative strategy. He’d have no way of reducing that list from the same six figures Bradshaw found. But Gamble’s detectives weren’t mathematical geniuses; Bradshaw was.

It was still an immense amount of data to review but Poe didn’t lose focus. His faith in Bradshaw was absolute; the answer was there somewhere. After he’d read a page, Bradshaw would take it from him and pin it to the wall in a pattern known only to her. It was a good idea. Looking at the montage gave a different perspective to looking at them individually. Of course, at some point they’d have to deal with the hotel manager’s wrath when he saw what they’d done to his freshly decorated wall, but that was a problem for another day. Or for Flynn. During a break to stretch his legs, Poe walked across to the flipboard the hotel had supplied and they had never used – Bradshaw frowned upon such technologically backwards tools – and picked up a marker pen from the tray underneath. He walked to the wall and started putting red crosses through vehicles he felt confident in ruling out.

Out of the 804 vehicles, over 30 were buses full of passengers. He put a red cross through them, doubting the Immolation Man had brought a coachload of supporters to his bonfires. He ruled out all the motorcycles; they might be able to go anywhere, but they couldn’t be used to transport victims, containers of accelerant and stakes. There were four minibuses, and although the pictures were small, Poe could see they were charities transporting adults with learning difficulties. He red-crossed them.

There were others he was happy to cross out as well. Police vehicles were an obvious one. It was possible the Immolation Man was a cop, but police vehicles weren’t used by one person; they did eight or ten hours with one shift, then would immediately be on the road with the next one. He crossed off ambulances for the same reason.

Next up were the prisoner-escort vans. The county’s tagline for years had been: ‘Cumbria: A Safe Place to Live, Work and Visit’, and, the Immolation Man aside, it usually was. But there was still a hard-core element of crooks and ne’er-do-wells, and although the number of courts had reduced, the number of idiots hadn’t. The GU Security vans were a regular sight on the Cumbrian roads as they serviced the county’s courts and its sole prison. But they were also shift vehicles. Poe put a red cross through them all.

He also red-crossed the bigger lorries. Although they’d have been ideal for transporting bodies and equipment, the winding routes to some of the killing sites ruled them out.

The number of pictures without red crosses was still unmanageable, though. Poe stood up and down on his tiptoes to stretch his calf muscles while he thought how he could reduce the number further.

He walked back to the wall and, in a fit of pique, red-crossed every car he thought was too small to comfortably transport a driver, a body and a can of petrol. When he’d finished he threw down the pen in frustration.

‘Sorry,’ he apologised. More for Bradshaw’s sake than Flynn’s.

‘You OK?’ Flynn asked.

He nodded.

‘Well, keep going. I think you’re onto something.’

He walked back to the flip chart and picked up a green pen. He ticked vehicles he wanted to prioritise. Any van with panelled sides got a green tick. Any estate car, four-by-four or MPV got a tick. There was even a hearse. That got a double tick.

Eventually every vehicle either had a red cross or a green tick. Some, after discussion, changed colour, but after an hour they had some sort of consensus.

Poe rocked backwards and forwards on his heels as he scrutinised the wall.

He was sure the answer was there. He just needed a spark of inspiration to find it.