Porter motioned for Styles to move down the right and he headed left. The room was an L-shape, the far leg of it disappearing round to the right. They attracted a few glances from the gym-goers but most were too busy preening in front of a mirror as they worked out. Of the dozen or so people he saw, only two of them were women. They both pounded out a beat on side-by-side treadmills, earbuds in, eyes front, ignoring the posturing alpha males.

The hidden leg of the room came into view slowly as Porter edged along the wall. Four exercise bikes lined up in a stationary peloton. A man in his forties pedalled furiously, rocking side to side as each leg extended, a bloom of sweat staining a grey Nike running vest.

No sign of Bolton. He turned to Styles, who shrugged back at him. Porter scanned the room. The only other door was marked Fire Exit, one with a horizontal push bar to open it. Styles came over to join him.

Porter spoke into his handset. ‘This is Porter. Be advised subject is not in the gym. He may be trying to exit the building. Proceeding through fire exit towards rear of the building.’

He pushed the bar down and the door swung open with no resistance, revealing a corridor with an identical fire exit door twenty feet away at the far end. He burst through it with Styles close behind, and almost ran straight into Anderson. They quickly disentangled from one another, and Porter stepped back.

‘Nothing?’ he asked.

‘No sign,’ said Anderson.

‘Sandford, Clarkson, anything?’ he barked into his handset.

‘Negative, guv,’ Sandford squawked back.

Whittaker stayed on the fire exit, and Sandford on the front door, while Porter led the others on a room-by-room search. Bemused customers and staff members watched as they opened every door and looked around every corner. Porter had to laugh despite his frustration when he saw Clarkson look under a desk. A man of Bolton’s size would be more likely to wear it like a tortoise wears a shell than squeeze underneath it.

Five minutes and another chat with the receptionist later, they stood out front. Porter stared at his own distorted reflection in the sleek black Mercedes.

‘He knew we were coming. That’s the only way. He knew we were coming.’

‘How could he, guv? We had the exits covered before we went in. Maybe he just left his car here while he went somewhere else?’ said Sandford.

Porter shook his head. ‘Nope, the receptionist saw him go into the gym about twenty minutes before we got here. If he left, he left out the back door, but he did it before we got here, and the only reason he would do that is cos he knew we were on our way.’

‘But how could he know? Has he got someone watching us?’ asked Clarkson.

‘Fuck knows, but he did,’ said Porter.