Despite having physically attacked him, the atmosphere between them as Mike left was the calmest it had been for almost a week, and they had agreed to talk again as soon as another opportunity came up.

Then she had set off in the car, following Amala’s directions until she reached the outskirts of Brentford as the two sergeants, still ten minutes ahead, watched Mardell’s car disappear inside the gates of a small, unused factory unit.

At that point Hawkins had rung off, telling her officers to park up somewhere they could keep tabs on Mardell without being seen, while she caught up the rest of the way.

Now she sat opposite what looked like a seventies shopping centre, covered in huge signs that blanked off the entire building, large white letters on black backgrounds.

Regenerating Brentford Town Centre.

‘I’m at the junction on the high street,’ she told Amala. ‘What street am I looking for?’

‘Dock Road, ma’am. It’s just north of the river.’

Hawkins checked her sat nav, seeing the Thames snake its way past her directly to the south, and the road Amala had mentioned, about two hundred yards to her left.

At last the lights let her go, and she swung out on to the main highway, passing a large supermarket before catching sight of the street sign. She turned on to Dock Road, a narrow thoroughfare hemmed in at first by tall brick buildings either side, but which opened out quickly to reveal factory units of various sizes set behind solid walls. Tarmac gave way to a patterned brick surface that rumbled beneath the Giulietta’s tyres.

‘I’m here.’ Hawkins leaned forwards, staring through the mist gathering on the inside of the screen. ‘Where are you?’

‘I see your lights,’ Amala said.

One of the vehicles parked in a row further along on the right flashed.

‘Stay there.’ Hawkins passed them and parked up, then walked quickly to the unmarked Vauxhall.

She slid into the back, leaning forwards between Amala and Aaron in the front seats. ‘Where is he?’

Amala pointed twenty yards ahead to a break in the wall. ‘He drove in there, fifteen minutes ago.’

Hawkins traced the perimeter beside them, seeing the top of an industrial unit that rose a short distance above the wall. ‘You said other cars went in, too?’

‘Yes, ma’am. There’s a barrier just inside, I saw it when we passed. They must have had someone manning it.’

‘Yeah,’ Aaron chipped in, ‘but what the hell are they doing in there?’

‘I don’t know,’ Hawkins told him, ‘but there’s only one way to find out.’