Hawkins could feel herself beginning to tire, the short but intense climb having taken its toll. Her heart pounded, but all she could hear was the rush of wind, and the crunch of her and Mike’s boots on the stones.

Which meant that here, on a busy overground track, where trains would pass through at regular intervals, she wouldn’t hear the inevitable sound of …

She glanced behind her, seeing the pinprick of light – splintered through watering eyes.

Silently coming closer.

She turned back, shouting at her partner. ‘Mike!’

He didn’t turn, clearly focused on catching Mardell, who had also stopped risking regular checks over his shoulder. Mike was only ten yards behind their suspect now, but Mardell was only fifty yards from the station. Hawkins was further back, and if they built any more of a lead, she risked being unable to warn him at all.

‘Mike!’

Still no response.

She thought fast, deciding after a few seconds to slow; not breaking stride as she bent to collect a few pebbles from the track. She straightened, drew back her arm and launched the first stone at her retreating colleague.

But her aim was off, and it dropped short.

She glanced back again. The train was closer this time, its bleary headlight having covered at least half the distance in the few seconds since she’d first identified the danger. It didn’t appear that the driver had yet noticed people on his track. Surely he would soon, but there was no guarantee he’d be able to stop in time. Obviously, the train would have some kind of horn, but that was only useful if the guy at the controls was paying attention.

She blinked, trying to knock the tears out of her eyes, straining as she ran onwards to establish which track the train was on. It was closing on them fast, no more than fifteen seconds from reaching them. Plus, they were on an unlit stretch of track, which meant the driver might not see them at all.

And as the train slid within a hundred yards of her position, a spark from the power lines allowed Hawkins to see it was using the outermost set of rails.

The track they were on.

Panic surged as she turned back towards the two men, judging that Mike was now fifteen yards ahead of her, and less than half of that behind Mardell.

She had to warn him.

She swerved on to the adjacent track, out of the train’s path, and stopped, panting hard. Then she hefted the stone in her palm, testing its weight, and took aim before launching it in a rapid arc towards her DI. It disappeared into the darkness.

The moment stretched, and Mike continued uninterrupted.

She had missed again.

For an instant, she heard nothing except the wind and her pulse. She couldn’t take her eyes off Maguire, feeling the steady pulse of panic switch to a torrent.