As on the phone, his tone was unusually truculent. He’d have a raft of paperwork to do following the door-to-door, of course, and after that Lucy wanted him to trawl the homeless shelters. He’d been here a while already, and no doubt envisioned yet another nine-till-five becoming another nine-till-nine, or maybe worse. She didn’t comment on that, because she understood his weariness at the prospect.

‘I need a wingman’ was all she said, walking past him through a gate in the steel-slatted fence, and taking the path on the other side.

He followed, hands in pockets, shoulders hunched. ‘I don’t get you.’

By rights, if they wanted to proceed from here they should have helmets on and protective clothing, but there was nobody around, and there was no time for that anyway.

‘We’re looking for a nun,’ she said over her shoulder.

‘A what?’

‘You heard me, Malcolm. A nun. A holy woman. Long black cassock, wimple, veil …’

‘I know what a nun is. I was raised a Catholic.’

‘Excellent … probably means you’ve got more chance of getting to Heaven than me.’

‘I just don’t know why I’d be looking for a nun out here.’

Lucy told him why as they walked, giving him the whole story. About how, despite her status as an inspirational teacher and mentor, Sister Cassiopeia had suffered a severe crisis of faith, which had led to an affair with a young priest and subsequent dismissal from her order. And about how her response to such disgrace had been to get into drugs, which in due course had conspired to transform the once beautiful nun into a homeless, smack-addicted prostitute.

‘Course, helping coppers is not a popular hobby among the downtrodden,’ Lucy said as they picked their way along a rutted track, the stink of the place already bunging up her nostrils. ‘But Cassie’s pretty much on our side. And in her case, it comes from the heart. It’s ironic, but since she’s been destitute, she’s rediscovered her belief. She’s adamant that right and wrong exist, she believes that hurting your neighbour is hurting God. Somehow, the rest of them respect that … they see her as an honest person. So they give her a pass.’

Lucy glanced at the encircling trash heaps. They were crisscrossed with caterpillar tracks, compressed into an undulant, colourless moonscape stretching as far as the eye could see, much of it pulverised to unrecognisable mulch. They were only a few hundred yards in, but it was already swarming with flies. Aggressive gulls swooped overhead.

Lucy also mentioned the van and what Sister Cassie thought she had seen and knew, including the other possible abductions. ‘We need to get it written down, Malcolm.’

‘You mean before Sister Cassie disappears too?’ He almost sounded hopeful that they’d already be too late.