It was half an hour before we were ready to leave, and we talked continually as we prepared. Toccata had been roped in to assist, despite her often erratic behaviour, which explained amongst other things why there were so many nightwalkers in the Cambrensis: she’d decided one day that no more would be retired or deployed, so had falsified the HotPot overheat to clear out the Cambrensis to make room. Quite how long they could be held there was never discussed, nor if this was a practical or well-thought-out policy – which it clearly wasn’t. But if it was a gut decision like the one I made about Birgitta, I totally got it.

Dr Gwynne was not coming with us. He viewed himself as being possessed of ‘Fortitude Lite’ but was good at technical support.

‘Good luck,’ he said as we were preparing to leave.

I thanked him and passed over a scribbled note.

‘I know this is a long shot,’ I said, ‘and the weather’s bad and everything, but I have a suggestion as to how you could redeploy at least one of the Golgothas to greater effect.’

He looked at the note and nodded slowly, then patted me on the shoulder, told me to take care, and we parted.

‘The plan is simple,’ said Foulnap as we walked down to the museum’s basement. ‘We go to the Siddons and retrieve the Somnagraph, then head to the Cambrensis for the cylinder. If anyone tries to stop us, we thump them.’

‘It has the benefit of simplicity.’

‘The best plans always do.’

The museum basement was used mostly for storage and contained a fairground ride, an entire Railplane tractor unit and half-scale educational models of a HotPot, both the closed thermosiphon and sintered hotplate version. There was also a collection of the now unfashionable hyperbaric deep-sleep chambers and a moth-eaten animatronic giant tree sloth, which had been doing the rounds as they were on the brink of extinction. More relevant to us there was a Welsh licence-built Sno-Trac branded a Griffin V, which looked as though it had just been pulled off display.

Foulnap instructed me to start her up and drive her out so I climbed in, my shock-suit more restricting than cumbersome. I hadn’t actually wanted to wear the one functioning suit, but Foulnap argued that since I was the most valuable, I should be the one inside it.

I settled into the Griffin, switched on the electrical systems, then pressed the air start and the engine hissed into life. Once Foulnap had opened and closed the double shock-doors, he joined me in the cab. It was now pitch black outside. The on-board anemometer registered gusts of sixty; the temperature was at minus forty, the only view from the headlights a bank of constantly moving snow.