“I paid particular attention to the path we took to the beach. I’m sure finding the cave again won’t pose a problem. Of course, I wouldn’t mind a volunteer to accompany me and lighten the load of my gear.”

“How much does your camera weight?” Rad quipped.

“My scuba gear, Rad.”

“You’re going diving in that lake?”

“The majority of merfolk sightings throughout the ages have been of the creatures in terrestrial environs—tidal flats, sandbars, rocky shores, and so forth. Which means, unlike whales and dolphins, they don’t spend one hundred percent of their lives in the water. They appear to be more akin to seals, which come ashore to mate or to escape predators or to simply rest and relax. And coming ashore on remote islands rather than continental land would have offered merfolk refuge from their more technologically advanced, and landlocked, hominin cousins. The first ocean-faring ships weren’t invented by modern humans until five thousand years ago, which is yesterday in geological timescales. Which is to say, merfolk would have been able to exist and evolve in isolation and safety for nearly two million years. What am I getting at?” He lit the tobacco in the bowl of his corncob pipe. “It’s always been a pet hypothesis of mine that merfolk don’t only live in the waters around islands but—”

“In submerged caves beneath islands,” Elsa finished, nodding thoughtfully.

“It would certainly explain why they’ve been so elusive over the centuries, wouldn’t it?”

Rad said, “And you think there are merfolk in that lake?”

“In the flooded lava tubes, yes, I think it’s a distinct possibility.”

Jacky said, “It would be pitch-black down there.”

“Which they could navigate perfectly fine with echolocation.”

“It’s an interesting premise, Marty,” Elsa said. “Yet I must ask, why would a presumably intelligent species choose to live in such a bleak environment?”

“Because the ocean is the most dangerous place on this planet, Elsa. Sharks and killer whales make the fiercest land predators seem tame by comparison. Just as early humans retreated to terrestrial caves for protection against giant birds and jaguars and bears, merfolk likely sought out underwater caves for the same reason.”

“Cave diving is not open water diving, mon capitaine,” Pip said. “It is dangerous and requires different training and equipment.”

“She’s right, Marty,” Rad said. “I don’t think you’ve thought this through completely.”

“I’m flattered by your concern, both of you. But rest assured, I’ve been on my fair share of cave diving expeditions throughout the British Isles, and I have the necessary equipment on board the Oannes to safely explore the lava tubes beneath Demon Island.”

“And what if you find merfolk, Marty?” Elsa said. “Or perhaps I should say, what if they find you? I can’t imagine they’d be thrilled by a surface-dwelling trespasser in their submarine domain?”