‘Jessie!’ he called again. ‘It’s Lieutenant Stride.’

They cleared the kitchen and the living room, which were both deserted. He used the remote control to switch off the television, restoring silence to the house, except for the rattle of the rotating floor fan. It was dim inside with the curtains closed. He pointed at the hallway, where he could see entrances to two bedrooms.

The first door was painted black, but it was open, and an overhead light was on. He nudged around the threshold into the bedroom, and the interior took his breath away. Maggie entered behind him.

‘Oh, shit,’ she said.

There was no bed, just a mattress on the floor. The walls, like the door, were painted black. The glass of the windows had been covered over with black plastic garbage bags duct-taped to the frame. A television sat on an old microwave stand in front of the mattress, and dozens of video games were strewn across the carpet. Gold ammunition littered the floor like popcorn. At least thirty bullet-ridden paper targets were thumbtacked to the wall, along with bizarre posters: a skeleton wearing a Nazi uniform; a naked girl with the head of a jackal and gun barrels for nipples; a skinless zombie in a diaper with blood spurting out of his face; and a Las Vegas casino street littered with torsos and severed limbs.

Across the entire wall, Ross had spray-painted in five-foot red letters: I AM GOD.

‘Jesus, who is this kid?’ Stride murmured.

But they knew who he was. They’d seen him before, in other cities, in schools, in workplaces.

Stride had made mistakes in his life. He’d arrested people who turned out to be innocent. He’d left cases unsolved. He’d failed to protect people he’d sworn to protect. This was different. This time, he’d missed a threat that Maggie had seen too clearly. That his wife had seen. He knew there was no bright line between social misfit and mass murderer, but he hadn’t seen this one coming.

Ross Klayman was out there somewhere. He was going to kill.

‘Where are the guns?’ Maggie asked. ‘Troy said Jessie had guns.’

They investigated the next bedroom, which was Jessie’s room. The gun locker was there, open and empty. No rifles. No handguns. No ammunition. Ross had taken everything when he left the house. If Troy was right, then Ross had an arsenal with him.

Stride saw Guppo in the doorway behind him.

‘Alert everybody, Max. Canal Park. Downtown. The mall. The DECC. He’s going to show up somewhere.’

Guppo turned away, already pulling out his walkie-talkie.

‘Boss,’ Maggie called. Her voice told him the story.