DC Shawcross tapped his keyboard, and a map of Potton Park and the surrounding area appeared on the white incident board, covering a four-mile radius. Kelly would be losing him to paternity leave shortly; his girlfriend Mia was due in early December but already ready to pop. It was appalling timing, but no one would feel worse about it than Rob. She’d have to make sure he stayed away should the case not be wrapped up by then, though he’d be sorely missed. He was their computer nerd and loved nothing more than creating logarithms and mapping aids to close down an investigation in its tracks. She had every faith in the rest of her team: young DC Emma Hide, who was all passion; DS Phillips, who lived and breathed protocol, and DS Umshaw, her battle-scarred workhorse.

Someone dimmed the lights, and Kelly picked up a long ruler and approached the board; her body became part of the map and she looked like a swamp dweller, covered in foliage and scarred earth.

‘The training session was here.’ She pointed to the glade in which the trainer had been giving a class to fourteen women. Their names and contact details had all been supplied and Kelly had uniforms tracking them down for statements. ‘Ella Watson was running this way.’ She indicated where Ella had collapsed and the direction from which she’d come. ‘If the trainer didn’t see anyone else, then the killers had to have come from the bushes here, or from this direction.’ She followed the ruler beyond the park. It was a direct line to the outskirts of the Beacon Estate.

‘I walked this route, past the pond, with the coroner this afternoon. It’s the most convincing theory. This area here is totally deserted and isolated. It’s just a few garages, but these flats here are the nearest residences.’

‘Boss, you said killers, plural? Is that now confirmed?’ DC Hide asked.

‘Not a hundred per cent. As you know, the coroner detected that the stab wounds were inflicted from two different directions. In his opinion – and I agree – it’s highly unusual for one perp to change position, especially during such a flash attack. He’ll confirm after the autopsy.’ Kelly paused. ‘What’s life on the Beacon Estate like these days?’

She watched as people shifted in their seats.

‘That bad? Will? You’ve got buddies in patrol units – you know, the ones you left behind to lord it about up here with us?’ It got a laugh and Will took it well. It was true, he had close ties to bobbies on the beat.

‘It’s not good, boss. It’s like shovelling shit while the horse is still having a dump, if you don’t mind the expression.’