‘It would really help,’ Townsend said. ‘If the phone finder app used the full GPS trace. If we had altitude, for example, we would instantly know which floor it was on.’

Perry and Claire Mulholland came back into the room, having been cleared of inadvertently carrying the phone. ‘Any progress?’ Perry asked.

‘Nope,’ Hoskins said, taking another spin around the room on his chair.

‘What about a drone?’ Perry asked. ‘It could have been dropped on the roof.’

‘Good thinking,’ Hoskins said. ‘I’ll take the lift.’

The detective constable was not fond of heights, and the flat roof of this, the highest building on the Mount Browne campus, reminded him of that fact. Keeping away from the two-foot high parapet at the edge, Hoskins made his way past the ranks of solar panels, looking underneath to see if anything had been deposited. The one place you couldn’t easily check was the top of the emergency exit onto the roof. There was an aluminium ladder screwed to the wall, but that was a bit too exposed for him. Besides, from the trace on the app, the phone should be roughly in the middle of the roof, not on one edge.

He was getting ready to go down, when he heard a car race into the car park. He looked across and spotted Gillard’s Vauxhall. It didn’t surprise him for a moment to see the detective chief inspector unable to stay away. By contrast old Radar Dobbs, despite being SIO, claimed to be working from home. Hoskins had had his run-ins with Gillard, and just a month ago had seen an attempt on the detective chief inspector’s life result in the death of his colleague DC Colin Hodges. But he trusted Gillard’s instincts like he trusted his own mother. The arrival of the best detective he had ever worked with gave him renewed confidence that they could crack the case.

At reception, Gillard confronted Ray Collins, a Mount Browne lifer with a gigantic beer belly and a fondness for sweets. Collins knew every officer in the building.

‘I can’t let you in, sir,’ Collins said. ‘I think you know why.’

‘It’s all right, Ray. But I understand there’s a kerfuffle about my wife’s phone being loose in the building.’

Collins sucked in his cheek. ‘I’ve no idea what is going on, and I guess I’m not supposed to talk to you about it. But yeah, there’s something happening.’

‘Is there anyone here who isn’t normally about?’

‘We’ve been through that, sir. Two guests from Essex Police, but they never even stayed in this block.’ He tapped a fat finger on the edge of the desk. ‘They had a meeting in forensics.’

Gillard looked around. ‘Get any post today?’

‘A bit, mostly internal. Some stationery from a commercial delivery.’ He indicated behind him a box that looked like printer paper, which had been shoved aside under a desk.

‘Just the one? Seems a bit odd.’

‘Who cares? The resource manager isn’t in until Monday. He’ll log it in and find out if it was what we expected.’