Whoever they were, they were being extremely quiet. Luce had almost decided that the crew must be asleep when she saw two figures slip out of the cabin. Both of them were as pitch black and sleek as the boat itself. One helped the other adjust what Luce guessed was some kind of oxygen tank. The glossy blackness enveloping them was their diving suits, then. Were they marine biologists, here to study creatures that only emerged at night? Luce froze behind the rock, keeping her head under the water and her body deep in the shadow thrown by the burning moon. Strange helmets with attachments Luce couldn’t identify covered the two figures’ heads; if they were seriously planning on diving this late they were probably wearing some kind of night-vision goggles. Any movement might attract their attention. She couldn’t even risk slipping to the surface to breathe, but with any luck they’d finish whatever they were doing here and go away before her air ran out. Luce could stay underwater for a long time if she had to.

One diver plopped overboard: a careful, vertical drop as if it was important to minimize the splash. Luce could just see the black body slicing down through the water, the flippers stirring as the diver began kicking deeper into the cove, angling toward the rough shelf of rock that walled one side. The other figure remained on deck, peering intently into the night away from Luce. Something about the moody, anxious tension of the figure on board began to worry Luce, and it suddenly occurred to her that these people were acting more like criminals than scientists. It didn’t make any sense, though. There was nothing in this desolate spot that any thief could possibly want.

The swimming diver had reached the rocks and seemed to be fiddling with them somehow, pulling back swags of seaweed and jamming or twisting an object that Luce couldn’t make out. The spot was deep enough that it would probably be underwater, though barely, at even the lowest tide.

A square patch of light suddenly gleaming off to the left made Luce swing her eyes back toward the boat. The figure on board had some kind of device out, bigger than a cell phone but smaller than a computer, with an oblong, glowing screen. Like that of all mermaids, Luce’s hearing was much sharper than a human’s. She could hear a quick tapping at some controls, see the figure nod in apparent relief. “We’re good, okay, we’re doing all right here . . .” a man’s voice mumbled, but something in the helmet distorted it into a staticky growl.

The diver was already kicking back to the boat with nervous speed, clambering up the side. The suited man still onboard stared fixedly at the screen, which was now giving out a darker glow, and didn’t move to help.