Kimo reeled the sensor back in. As he pulled it from the water, something odd caught his eye. He squinted. A hundred yards off, a strange black sheen was spreading across the ocean surface like a shadow.

“Check this out,” he said to Thalia.

“Stop trying to get me up there in close quarters,” she joked.

“I’m serious,” he said. “There’s something on the water.”

She put down the computer tablet and came forward, putting a hand on his arm to steady herself on the narrow bowsprit. Kimo pointed to the shadow. It was definitely spreading, moving across the surface like oil or algae, though it had an odd texture to it unlike either of those things.

“Do you see that?”

She followed his gaze and then brought a pair of binoculars to her eyes. After a few seconds, she spoke.

“It’s just the light playing tricks on you.”

“It’s not the light.”

She stared through the binoculars a moment longer and then offered them to him. “I’m telling you, there’s nothing out there.”

Kimo squinted in the failing light. Were his eyes deceiving him? He took the binoculars and scanned the area. He lowered them, brought them up and lowered them again.

Nothing but water. No algae, no oil, no odd texture to the surface of the sea. He scanned to both sides to make sure he wasn’t looking in the wrong place, but the sea looked normal again.

“I’m telling you, there was something out there,” he said.

“Nice try,” she replied. “Let’s eat.”

Thalia turned and picked her way back toward the catamaran’s main deck. Kimo took one final look, saw nothing out of the ordinary, then shook his head and turned to follow her.

A few minutes later they were in the main cabin, chowing down on fish tacos Halverson style while laughing and discussing their thoughts as to the cause of the temperature anomaly.

As they ate, the catamaran continued northwest with the wind. The smooth fiberglass of its twin bows sliced through the calm sea, the water slid past, traveling silently along the hydrodynamic shape.

And then something began to change. The water’s viscosity seemed to thicken slightly. The ripples grew larger and they moved a fraction slower. The brilliant white fiberglass of the boat’s pontoons began to darken at the waterline as if being tinted by a dye of some kind.

This continued for several seconds as a charcoal-colored stain began spreading across the side of the hull. It began to move upward, defying gravity, as if being drawn by some power.

A texture to the stain resembled graphite or a darker, thinner version of quicksilver. Before long, the leading edge of this stain crested the catamaran’s bow, swirling in the very spot where Kimo had stood.

Had someone been watching closely, they would have noticed a pattern appear. For an instant the substance shaped itself like footprints, before becoming smooth once again and slithering backward, headed toward the main cabin.

Inside the cabin, a radio played, picking up a shortwave broadcast of classical music. It was good dinner music, and Kimo found himself enjoying the evening and the company as much as the food. But as Halverson fought against divulging the secret of his taco recipe, Kimo noticed something odd.

Something was beginning to cover the cabin’s broad tinted windows, blocking out the fading sky and the illumination from the boat’s lights high up on the mast. The substance climbed up the glass the way wind-driven snow or sand might pile up against a flat surface, but much, much faster.

“What in the world …”

Thalia looked to the window. Halverson’s eyes went the other way, glancing out at the aft deck with alarm on his face.

Kimo swung his head around. Some type of gray substance was flowing through the open door, moving along the deck of the boat but flowing uphill.

Thalia saw it too. Heading straight for her.

She jumped out of her seat, knocking her plate from the table. The last bites of her dinner landed in front of the advancing mass. When it reached the leftovers, the gray substance flowed over the bits of food, covering it completely and swirling around it in a growing mound.

“What is that?” she asked.

“I don’t know,” Kimo said. “I’ve never …”

He didn’t have to finish his sentence. None of them had ever seen anything like it. Except …

Kimo’s eyes narrowed, the strange substance flowed like a liquid, but it had a grainy texture. It seemed more like metallic powder sliding across itself, like waves of the finest sand shifting in the wind.

“That’s what I saw on the water,” he said, backing away. “I told you there was something out there.”

“What’s it doing?”

All of them were standing and easing backward.

“It looks like it’s eating the fish,” Halverson said.

Kimo stared, vacillating between fear and wonder. He glanced through the open door. The rear deck was covered.

He looked around for a way out. Moving forward would only take them down into the catamaran’s berths, trapping them. Going aft would mean stepping on the strange substance.

“Come on,” he said, climbing onto the table. “Whatever that stuff is, I’m pretty sure we don’t want to touch it.”

As Thalia climbed up beside him, Kimo reached toward the skylight and propped it open. He gave her a boost, and she pulled herself up through the opening and onto the cabin’s roof.

Halverson climbed onto the table next but slipped. His foot slammed into the metallic dust, splashing it like a puddle. Some of it splattered onto his calf.

Halverson grunted as if he’d been stung. Reaching down, he tried to swipe it off his leg, but half of what he swiped clung to his hand.

He shook his hand rapidly and then rubbed it on his shorts.

“It’s burning my skin,” he said, his face showing the pain.

“Come on, Perry,” Kimo shouted.

Halverson climbed up on the table with a small amount of the silvery residue still clinging to his hand and leg, and the table buckled under the weight of the two men.

Kimo grabbed the edge of the skylight and held on, but Halverson fell. He landed on his back, hitting his head. The impact seemed to stun him. He grunted and rolled over, putting his hands down on the deck to push off with.

The gray substance swarmed over him, covering his hands, his arms and his back. He managed to get up and brace himself against the bulkhead, but some of the residue reached his face. Halverson pawed at his face as if bees were swarming around him. His eyes were shut tight, but the strange particles were forcing themselves under his eyelids and streaming into his nostrils and ears.

He stepped away from the bulkhead and fell to his knees. He began digging at his ears and screaming. Lines of the swarming substance curled over his lips and began flowing down into his throat, turning his screams into the gurgles of a choking man. Halverson fell forward. The spreading mass of particles began to cover him as if he was being consumed by a horde of ants in the jungle.

“Kimo!” Thalia shouted.

Her voice snapped Kimo out of his trance. He pulled himself up and scrambled through the opening onto the roof. He shut the skylight and sealed it hard. From the spotlights high in the mast he could see that the gray swarm had spread across the entire deck, both fore and aft. It was also creeping upward along the sides of the cabin.

Here and there it seemed to be swarming over things as it had done to the fallen dinner items and Halverson.

“It’s coming up over here,” Thalia shouted.

“Don’t touch it!”

On his side the invading swarm had made less progress. Kimo reached over and grabbed for anything that would help. His hand found the deck hose and he turned it on, grabbing the nozzle and spraying high-pressure water at the gray mass.

The jet of liquid swept the particles backward, washing them off the cabin’s wall like mud.