Alice eased the door open, hoping it wouldn’t creak. It swung inwards silently, revealing a short corridor and the stairway where she’d perched the swarmer. In the flickering gaslight she saw a large, square room at the bottom, crowded with bushels and crates of stuff – baskets of nails, crates of soap-flakes, huge bottles of oil and cleansers, wrapped bundles of candles. At the back of it, the door to the furnace room was open, letting out a dull red glow that bathed the stone-flagged floor in crimson light. As she watched, a shadow moved across it.

‘He’s in there,’ she whispered to Isaac.

‘All right.’ Isaac peered doubtfully down the stairs. ‘So you’ll distract him, and I get in there.’

‘Right.’

‘Let’s hope he hasn’t hidden it, or locked it up.’ Isaac got an odd, faraway look in his eyes for a moment, as though staring at something on the far side of the wall. ‘I’m ready.’

Alice nodded tightly. She took the staircase one step at a time, wary of any noise. Once she reached the bottom, she crept around the piles of supplies to the opposite corner of the room, where she’d be out of view from the furnace-room doorway.

She closed her eyes and reached out, and found the silver thread of the Swarm waiting. Gathering it up, she gave a gentle tug, and a half-dozen swarmers popped quietly into existence by her feet. They greeted her with a chorus of quirks, which she stilled with a hasty mental command.

Carefully, she extended her vision into one of them, keeping her real eyes closed. She navigated the swarmer around the pile of supplies and towards the door to the furnace room, ordering the others to follow a few paces behind. The little bird-like creature scurried across the floor until it had a good view of Mr Black, sitting at his workbench and working on something with a pair of heavy iron clippers. From her point of view a few inches off the ground, she couldn’t see the top of the table.

The swarmer crept closer, until it was only a few feet from the huge man. Before she could go any further, he gave an enormous snort and shoved his chair back from the workbench, one enormous hand coming down with shocking speed to snatch the swarmer off the floor. Alice felt a moment of sheer terror and had to remind herself that it was not her actual physical body in danger. One of the swarmer’s eyes had a close-up view of Mr Black’s hairy, pockmarked face, and the trails of smoke leaking from his nostrils.

‘What have we got here?’ he said, his voice echoing oddly as it came both through the swarmer and through Alice’s real ears. ‘What in the Pit are you supposed to be?’