“I’ve been analyzing the sonar data. The pod of dolphins has apparently lost interest in us and moved on, leaving this neck of the ocean oddly quiet. Ah, a full moon. My favorite lunar phase.”

“It makes you feel small, doesn’t it?”

“The moon? Sure. It’s a large celestial body, after all.”

“The moon, the stars, space…” They were silent for a few moments, and then Elsa added, “This might sound strange, but the moon is why I became an oceanographer in the first place.”

“You do know there’s no water up there, right?”

“Did you believe your mother when she told you there was a Man in the Moon?”

“I don’t imagine she ever told me such a thing. She is a rather sensible woman.”

“My mother told me there was a Man in the Moon, and I believed her. I used to think he could see everything that I did. When I said my prayers, I often included him in them, telling him I was sorry for doing this or that. Even when I grew older, and learned the image of the human face was just various lunar maria, the moon retained a special place in my heart. In fact, as a teenager I wanted to become an astronaut. That dream fizzled out in university when I learned that qualified applicants had less than a half-percent chance of being selected by NASA.”

“Astronomical odds.”

“Funny, but yes. I didn’t have a realistic hope in hell. So to scratch my itch for exploration, I turned my attention to the oceans. And here I am some twenty years later—cataloguing whale shit. Can you see those black dots on the moon?”

“The craters?”

“No, the much smaller pockmarks. They’re the skylights of collapsed lava tubes.”

“Must be damn big lava tubes.”

“Some are more than a mile in diameter and twenty times that in length.”

“Why are they so much bigger than the lava tubes on earth?”

“The lower gravity affects volcanism differently there. It also keeps the lava tubes in remarkably good shape. Scientists are talking about how future astronauts could use them as shelter from the harsh environment, fluctuating temperatures, and radiation. It’s interesting—prehistoric humans started out in caves on earth, and when we establish permanent settlements on the moon, we’ll be starting out in caves all over again. I wanted to ask you something, Marty. Would you consider putting off your dive beneath Demon Island for another day or so?”

He frowned. “Whatever for?”

“I would like to accompany you.”

“Accompany me?” He shook his head. “I’m sure you’re an accomplished scuba diver, Elsa. But as Pip mentioned earlier, cave diving is not your typical recreational dive.”

“I’m well aware of the dangers, Marty,” she said firmly. “I’ve logged hundreds of dives and thousands of hours in underwater caves throughout the Americas.”

He blinked in surprise. “Is that so?”