“I guess I’m coming along too then,” Jacky said. “After you, Marty. And try not to trip and break your ankle, because Rad and I aren’t strong enough to carry you back out.”

They didn’t have to worry about tripping on anything, as the floor of the cave was unnaturally smooth and free from typical rocky debris. Marty realized it was not a limestone cave but a volcanic lava tube. When the volcano in the center of Demon Island erupted however many thousands of years ago, the surface of the flowing lava would have inevitably cooled and crusted to form a roof above the still-flowing stream of molten rock, and when the last of the lava drained away, all that remained behind were empty, snaking tunnels.

And if I’m not mistaken, Marty thought excitedly, some of the tunnels most certainly connect with the ocean, making the discovery of merfolk bones a distinct possibility after all.

Soon the tunnel opened to a cavernous hall with twenty-foot ceilings. It appeared to be a dead end, but the chief went confidently to the left side, where there was a small fissure in the wall. The passage was so tight they were forced to duckwalk and shimmy through. They emerged in another large tunnel in which they could once again walk comfortably upright and abreast of one another. They knew they were still close to the surface because here and there tree roots broke through the tunnel roofs, dangling down like spidery appendages.

After progressing for several minutes with only the torchlight to see by, Marty suddenly made out a different light source in the distance, which turned out to be sun shining through a section of collapsed ceiling. Verdant jungle rimmed the edge of the hole, which was the size of a baseball diamond. Tangles of vines dripped to the cavity floor. The light filtering through the canopy far above them was much brighter than the torchlight, revealing the solidified drips and waves the lava had scoured into the tunnel walls, as well as the many different minerals coloring the igneous rock.

Jacky and Rad oohed and aahed at the sights and seemed ready to take a break, but the chief had other plans, climbing over the scree and continuing onward.

For the next five hundred meters the lava tube remained so straight and uniform it would have been easy to believe it had been manmade. The chief pointed out several large holes in the floor, deep shafts that would connect to lower-level tunnels, and they all steered clear of them. And then light appeared in the distance again. The source turned out to be another skylight, yet unlike the previous section of broken tunnel, here the ground disappeared beneath a perfectly still subterranean lake.

“I knew it!” Marty cried triumphantly, joining the chief at the water’s edge. “The tunnel connects with the ocean! I bloody well knew it!”

The chief pointed at the water and said, “Where.”