Lucy throttled forward, hitting the top of the ramp at 35mph and hurtling down it forty yards or so, her headlamp spearing through the darkness, flooding over a mound of white, dusty rubble lying across her path. At some point in the past, a concrete pillar had toppled across the foot of the ramp, bringing down a mass of masonry, which now formed a barrier impassable to a four-wheeled vehicle.

But not to a bike.

She slowed again, but the rubble wasn’t steep and was loosely compacted, which gave her an easier tread. She wove her way up it, arriving on the top and braking hard.

The glare of her light now revealed a much larger cellar than she’d expected, an unloading area of some sort. It was fifty by sixty yards, and almost entirely concrete, much of it cracked or water-stained, the many pillars holding up its ceiling scrawled with incomprehensible graffiti. There was plenty more evidence that folk had been sleeping down here; she saw blackened braziers, stained mattresses, food cartons, but the only two people present were in the very centre of the underground space, engaged in what looked at first like a violent dance.

One of them, by her spinning, tattered skirts and the fact that her veil had come off, allowing a mop of damp red-grey hair to billow free, was Sister Cassie. The other, her assailant, was younger, leaner and wearing what looked like black combat fatigues complete with boots and gloves, and a harness to which weapons were visibly attached.

To Lucy’s incredulity, this second person, who’d snatched the ex-nun by her front collar with one hand and was aiming punches at her with the other, looked female. That was the only impression that could be gleaned from the blonde, sweat-slick hair flying around her head, though it was difficult to be absolutely sure, as she ducked and weaved in her efforts to avoid retaliatory blows from Sister Cassie.

Lucy cut her engine. ‘Police officer!’ she bellowed. ‘What’s going on here?’

The blonde girl responded quickly, jumping ramrod-straight, glaring in Lucy’s direction. She’d clearly noticed when the glow of the headlamp had appeared over the pile of rubble, but perhaps, in the midst of combat, had mistaken it for her confederate’s vehicle. Now the light caught her full-on, revealing what looked like extensive facial injuries. At the same time, it distracted her, and she caught a left-hand swing from Sister Cassie hard on her left cheek, which drew a squawk of rage and pain. She replied with a vicious punch, hacking it into Sister Cassie’s ribs, doubling her down to her knees, and then, after kicking her in the side and sending her sprawling, running towards a distant doorway.