Before Lucy could speak, Alyssa pointed her pistol one-handed and pumped its trigger. A succession of metallic clicks followed. The girl’s swollen, sweat-soaked face twisted with fury and disgust, but she threw the empty gun away and came on regardless, this time reaching into the combat webbing at her back and pulling out a huge knife. It was the same type of weapon that Ivana had wielded, the same type of weapon Alyssa herself had produced in the cellars at St Clement’s, with a medieval-style cross-guard and a heavy blade serrated down one edge. Alyssa raised it in her right hand as she approached, holding it upright, a gesture designed to show that she knew how to use it.

Lucy had been considering fighting the teenager, trying to overpower her physically. But she had no doubt that Alyssa’s father had trained her well. Plus, there was this knife.

‘I’m going to enjoy this,’ the girl drooled. ‘I’m so going to enjoy this.’

Lucy darted right, trying to run along the narrow band of bricks edging the rooftop, but her feet slipped, and she almost pitched into the abyss, only preventing it by sliding to a stop and windmilling her arms. Alyssa continued her pursuit at a walking pace but snickered. ‘You are so out of your depth …’

Lucy was starting to think this was true. It was impossible to describe how tired she felt. She had no weapons with which to resist. All she could do was turn and back away, veering across the tar-coated planking, hoping to God that it wouldn’t simply collapse and drop her down into some empty, dust-filled dormitory.

When it didn’t, she ran again, heading across the roof towards the other side. Who knew, she might find the top of a fire-escape stair. Or perhaps there’d be ivy she could clamber down.

Yeah, right.

She came to the next parapet more quickly than she’d expected, finding herself high above a central courtyard, where vegetation grew wild and jungle-like from a central quadrangle surrounded by paved walkways and benches. Again, it was an eighty-foot drop, and there was no means of descent. The nearest window ledge was a good twenty feet down, and no more than a couple of inches wide.

‘Why don’t you do it?’ Alyssa taunted her, advancing across the roof in slow pursuit, breathing more easily now, clearly regaining her stamina, and still holding her blade aloft. ‘It’d be quicker than what I’ve got planned for you.’