We did not need torches at first, though it was fairly gloomy. The air was stuffy and heavy with the smell of long-dead things. The water was freezing, and my toes were soon numb, followed soon after by the rest of my feet. Fortunately the streambed provided a firm and even footing, and in spite of a moderately strong current we were in no danger of slipping.

If we looked back – and I did several times – we could see the entrance to the tunnel and the sunlight outside. But the light grew fainter, the tunnel mouth smaller. Finally Matt switched on his torch, and in its beam we could see the tunnel continue as far as the light reached. It was, however, not as high as it had been, and my back was beginning to complain – not just at carrying a pack again, but having to do it in such an awkward, bent-over position. I felt like suggesting a rest, but I didn’t really want to stop anywhere Hairy Legs might sight us from the outside.

We must have kept going for fifteen minutes or more. It was pitch black without the torches – Matt had switched his off for a moment before I had got mine going – and time and space were both difficult to keep hold of. The single improvement was that the water had got shallower, and there was a narrow bank now on either side of the tunnel.

“Anyone want a break?” asked Matt.

Slick and I chorused our approval, and we perched our backsides on the narrow dry strip, our packs pressed against the tunnel wall, our feet still in the water. Matt switched his torch off, but I left mine on. Apart from our breathing the silence was absolute. Even the stream ran without sound. I was just getting nicely drowsy when Matt stood up and, wordlessly, led us on again.

The tunnel got no narrower, but its height was steadily growing less and even Slick had to stoop now. It made for very uncomfortable travel.

“How far up do you want to go?” I asked Matt.

His voice came back muffled, as he could not turn. “As far as we can – this water must come from somewhere.”

I thought we had already gone as far as we reasonably could, but this did not seem to be the time to mention it. Matt can be very deaf sometimes. At last even Matt could not stand the agony of walking doubled over any more. Without asking us, he sat down and began to ease his pack off. We did the same. Matt scratched Stripes between the ears thoughtfully.