She moved to a shoulder-high stone shelf, which already looked to be cluttered with bits and pieces: among numerous other items, Lucy saw false teeth, a medal with a faded ribbon, an old-fashioned hearing aid. Alyssa carefully placed the beaker down among them, and then returned and violently searched Lucy’s jacket pockets. Almost immediately, she found the wallet containing her warrant card. She flipped it open and showed it to her sister. ‘Her pig ID.’

‘That’ll do nicely,’ Ivana said.

Alyssa went back to the shelf and made room among the other oddments. The fumes were visibly affecting her: she coughed, her face gleaming with sweat, her eyes running, though it mainly served to make her triumphant grin seem all the more deranged.

‘What do you think of this stuff, DC Clayburn?’ She held things up one by one. ‘An old guy’s hearing aid. The Cat Lady’s false teeth.’ There was even a pair of colourful running shoes. ‘Don’t need to tell you who these belonged to. UltraBoost, too. Would’ve been a shocking waste putting those in the acid.’ She folded Lucy’s wallet backwards, so that it would stand open on the warrant card, and then placed it directly alongside another that was very similar to it. ‘Matching pair, eh? You and that young rookie you sent ahead of you. Looks like we got ourselves a couple of Category As tonight … without getting a kicking in the process.’

‘We’re doing you a favour, showing you all this,’ Ivana whispered into Lucy’s ear. ‘We’re letting you know that at least there’ll be something left to remember you both by.’

Lucy struggled, only for her captor to twist and tighten the tourniquet. Lucy’s eyes goggled, her tongue lolling.

‘No – you – don’t,’ Ivana chuckled. ‘I know it hurts, but that’s the whole point.’

Alyssa, meanwhile, had moved to the nearest of the two drums and, holding a cloth to her mouth with one hand, now held a thick plastic rod in the other and was using it to stir the contents.

‘This stuff’s viscous,’ she complained. ‘It’s more like sludge.’

‘It’s ready for pouring,’ Ivana replied. ‘Try the other one.’

Alyssa moved to the second drum and, with a huge effort, dislodged its stone lid. Again, the chemical reek filling the air intensified. Lucy felt her eyes stinging.

Alyssa coughed all the more. ‘Yeah, this is better …’

With Ivana distracted, her grip on the tourniquet lessened slightly, and Lucy could drag some air into her lungs. Revived, she didn’t try to yank the ligature loose now, but rent at her own clothes, searching for anything she could.