Then she thought she heard something; the screech of a metal door being forced. She glanced back along the arcade, thinking that she would easily see someone approaching her from behind. The passage had curved, however, so that the last noisy door she had come through was out of sight. Of course, if someone was following her – she couldn’t help thinking about that crouching, apelike figure – it wasn’t necessarily the best idea to hang around and meet them.

She decided to head back now. This had clearly been a futile errand. She had other work to attend to anyway and would simply put out a BOLO, or ‘Be on the Lookout’, for Sister Cassiopeia. A steel-framed doorway a few yards away looked most promising. When she glanced through it, she saw another brick corridor, but with light at the far end. However, she was no more than five yards inside when she realised that a dark figure was coming down it towards her. It came quickly but awkwardly, moving with a horrible seesawing gait; the closer it got, the more of the light at the end it blotted out.

Lucy backed stiffly into the moonlight, thinking that if someone was behind her as well, she might be cut off. Her hands slid under her jacket, fingers caressing the hilt of the baton. She could now hear whoever this was; feet clumping, damp material whisking over bricks and concrete. Before she knew it, she’d retreated to the other side of the arcade. Where once there’d been a timber wall, now there was a drop of seven or eight feet onto heaps of burned, mangled rubbish. Her heels were right on the edge, and she was tottering.

She stopped, risked a glance behind, and then looked back across the arcade – just as a voluminous shape, cowled and cloaked in black, ballooned into sight.

Lucy half-sagged with relief.

Sister Cassie briefly managed to look even more ghostlike than usual, hobbling forward through the moonlight rather than gliding gracefully as she usually did. Consternation was written on her face.

‘Lucy, Lucy,’ she said admonishingly. ‘I’d heard you’d come here looking for me. For Heaven’s sake, child, whatever possessed you to come into this place on your own?’

Lucy released the baton back into its pouch. ‘I told you I’d come and find you.’

‘Yes, but this dreadful place isn’t safe for a girl like you. Not at night.’

‘Sister … I’m a police officer.’

‘And that’s something else that worries me.’ The ex-nun tut-tutted, eyeing her up and down. ‘A child like you … in a job like this.’

‘Sister …’ Lucy suppressed her irritation. ‘Your concern is appreciated. But if it’s safe enough for you …’