Alex climbed down the wall like a spider; there were enough protrusions to afford him plenty of hand and toe holds and his caving suit was specially toughened on the fingers and toes for just such a climb. He was confident that Monica could have ascended without trouble, but it would have cost them at least another ten minutes and at this point Alex was keen to save every second they had and use it for escape.

Monica shone her torch in a slow arc around them. Caves were amazing places. There were magnificent formations all around and above them; straw-like calcite stalactites and huge piles of what looked like frozen pink froth lumped around like melted candy. As a general rule, the larger the cave, the older it was. By that standard, these caves were truly prehistoric. It was like being in some giant child’s garden made from coloured stone. Rocks that looked like icicles, trees, statues, or the delicate designs of lacy flowers in shades of white or cream, or blues and reds from the dissolved minerals trickling from miles of stone overhead. At any other time Monica would have been lost in delight at this caving wonderland—for now, survival was the priority.

The cave ended abruptly at the bank of a wide and slow-moving river. It looked shallow, but cave pools and streams could be deceptive due to the clarity of the water—a stream where you could easily pick out every tiny pebble on its bottom could actually be over six feet deep. The upside was that there were rarely hidden jagged objects under the surface—the smoothing effect of thousands of years of polishing by the moving liquid.

“What now, build a boat from rocks?” sneered Silex. It was an obnoxiously posed question, but they were presented with a problem—they had no raft and there was no river bank or beach to walk along. They couldn’t cross to the far side of the river as it ended in a sheer rock wall—in fact, the cave they were in ended at the river.