I found the road with the railing, and steered the big car up the slope and on to a cobbled esplanade.

It was easy enough to see now why the girl with the piece of coal in her mouth had been so amused, for what met my eyes was no more what one would normally have recognized as a schoolhouse, than a zoo was a pet-shop, or a cathedral a meeting hall. Himmler’s schoolhouse was in reality a decent-sized castle, complete with domed towers, one of which loomed over the esplanade like the helmeted head of some enormous Prussian soldier.

I drew up next to a small church a short distance away from the several troop trucks and staff cars that were parked outside what looked like the castle guard-house on the eastern side. For a moment the storm lit up the entire sky and I had a spectral black-and-white view of the whole of the castle.

By any standard it was an impressive-looking place, with rather more of the horror film about it than was entirely comfortable a proposition for the intendant trespasser. This so-called schoolhouse looked like home from home for Dracula, Frankenstein, Orlac and a whole forestful of Wolfmen — the sort of occasion where I might have been prompted to re-load my pistol with nine millimetre cloves of snub-nosed garlic.

Almost certainly there were enough real-life monsters in the Wewelsburg Castle without having to worry about the more fanciful ones, and I didn’t doubt that Himmler could have given Doctor X quite a few pointers.

But could I trust Heydrich? I thought about this for quite a while. Finally I decided that I could almost certainly trust him to be ambitious, and since I was effectively providing him with the means of destroying an enemy in the shape of Weisthor, I had no real alternative but to put myself and my information in his murdering white hands.

The little church bell in the clock-tower was striking midnight as I steered the Mercedes to the edge of the esplanade and beyond it, the bridge curving left across the empty moat towards the castle gate.

An S S trooper emerged from a stone sentry-box to glance at my papers and to wave me on.

In front of the wooden gate I stopped and sounded the car horn a couple of times. There were lights on all over the castle, and it didn’t seem likely that I’d be waking anyone, dead or alive. A small door in the gate swung open and an S S corporal came outside to speak to me. After scrutinizing my papers in his torchlight, he allowed me to step through the door and into the arched gateway where once again I repeated my story and presented my papers, only this time it was for the benefit of a young lieutenant apparently in command of the guard-duty.