“Unless he’s secretly studied German and medicine,” Grossbaum said, “he’s not remembering anything from before.” He told them about idiots savants, who had astonishing mental powers in some narrow specialty, but otherwise couldn’t function normally. But he’d never heard of anyone changing from a normal person into an idiot savant; he promised to look into it.

Jimmy’s progress in less intellectual realms was fast. He no longer was clumsy walking around the house and grounds—at first he hadn’t seemed to know what doors and windows were. Lowell and Deborah taught him badminton, and after initial confusion he had a natural talent for it—not surprising, since he’d been the best tennis player in his class. They were amazed at what he could do in the swimming pool—when he first jumped in, he did two rapid lengths underwater, using a stroke neither of them could identify. When they demonstrated the Australian crawl, breast stroke, and backstroke, he “remembered” them immediately.

By the second week, he was taking his meals with the family, not only manipulating the complex dinner service flawlessly, but also communicating his desires clearly to the servants, even though he couldn’t carry on a simple conversation.

His mother invited Dr. Grossbaum to dinner, so he could see how well Jimmy was getting along with the help. The psychiatrist was impressed, but not because he saw it as evidence of growth. It was like the facial nerves and German poetry; like badminton and swimming. The boy could imitate anybody perfectly. When he was thirsty, he pointed at his glass, and it was filled. That was what his mother did, too.

His parents had evidently not noticed that every time a servant made a noise at Jimmy, he nodded and smiled. When the servant’s action was completed, he nodded and smiled again. That did get him a lot of food, but he was a growing boy.

Interesting that the nurses’ records showed no change in weight. Exercise?

It was unscientific, but Grossbaum admitted to himself that he didn’t like this boy, and for some reason was afraid of him. Maybe it was his psychiatric residency in the penal system—maybe he was projecting from that unsettling time. But he always felt that Jimmy was studying him intently, the way the intelligent prisoners had: what can I get out of this man?

A better psychiatrist might have noticed that the changeling treated everyone that way.

Apia, independent Samoa, 2019

It takes a long time for cement to cure in the tropics, and the artifact stayed floating offshore, shrouded, for two weeks while the thick slab, laced with rebar, slowly hardened. They knew that no conventional factory floor could support the massive thing without collapsing. It was the size of a small truck, but somehow weighed more than a Nautilus-class submarine: five thousand metric tonnes. It would be three times as dense as plutonium, if it were a solid chunk of metal.

Halliburton had started to let his beard and hair grow out the day he retired his commission. The beard was irregular and wispy, startling white against his sun-darkened skin. He had taken to wearing gaudy Hawaiian shirts with a white linen tropical suit. He would have looked more dapper if he didn’t smoke a pipe, which accented his white clothes with gray smudges of spilled ash.

Russell regarded his partner with a mixture of affection and caution. They were waiting for lunch, sipping coffee on a veranda that overlooked the Harbour Light beach.

The morning was beautiful, like most spring mornings here. Tourists sunned and strutted on the dark sand beach, children laughed and played, couples churned rented dugouts with no particular skill in the shallows over the reef, probably annoying divers.

Russell picked up a small pair of binoculars and studied a few of the women on the beach. Then he scanned the horizon line to the north, and could just make out a pair of fluttering pennants that marked their floating treasure. “Did you get through to Manolo this morning?”

Halliburton nodded. “He was headed for the site. Says they’re going to test the rollers today.”

“What on earth with?”

“A couple of U.S. Marine Corps tanks. They went missing from the Pago Pago armory, along with a couple of crews. You want to know how much they cost?”

“That’s your department.”

“Nada. Not a damn thing.” He chuckled. “It’s a mobilization exercise.”

“Convenient. That colonel we had dinner with, the Marine.”

“Of course.” Three waiters brought their meal, two piles of freshly sliced fruit and a hot iron pan of sizzling sausages. Halliburton sent away his coffee and asked for a Bloody Mary.

“Celebrating?”

“Always.” He ignored the fruit and tore into the sausages. “The test should commence at about 1400.”

“How much do tanks weigh?” Russell served himself mango, pawpaw, and melon.

“I’d have to look it up. About sixty tons.”

“Oh, good. That’s within a couple of orders of magnitude.”

“Have to extrapolate.”

“Let’s see.” He sliced the melon precisely. “If a two-pound chicken can sit on an egg without harming it, let’s extrapolate the effect of a one-tonne chicken.”

“Ha-ha.” The waiter brought the Bloody Mary and whispered, “With gin, sir.” Halliburton nodded microscopically.

“It’s not exactly Hooke’s law,” Russell continued. “How can you get a number that means anything?”

Halliburton set down his silverware and wiped his fingers carefully, then took a pad out of his shirt pocket. He tapped on its face a few times. “The Wallace-Gellman algorithm.”

“Never heard of it.”

He adjusted the brightness of the pad and passed it over. “It’s about compressibility. The retaining plates we drove down into the sand. It’s actually the column of sand supporting the thing’s mass, of course.”

“A house built on sand. I read about that.” Russell studied the pad and tapped on a couple of variables for clarification. He grunted assent and passed it back. “Where’d you get it?”

“Best Buy.”

He winced. “The algorithm.”

“California building code. A house built on sand shall not stand without it.”

“Hm. So how much does an apartment building weigh?”

“We’re in the ballpark. It’s going to settle some. That’s why the moat-and-dike design.”

“If it settles more than five meters, we won’t have a moat. We’ll have an underwater laboratory.” Once the thing was in place, the plan was to put a prefabricated dome, five meters high, over the thing, dig a moat around it, and then build a high dike around the moat. (If it settled more than a couple of feet, water would seep around it at high tide anyhow. The moat made that inevitability a design feature.)

“Won’t happen. It was in sand when we found it, remember?”

Not volcanic sand, Russell thought, but he didn’t want to argue it. The coral sand wasn’t that much more compressible, he supposed. He signaled the waiter. “Is it after noon, Josh?”

“Always, sir. White wine?”

“Please.” He reached over the fruit and speared a sausage.

“So when do we expect the tanks?”

“They said 1300.”

“Samoan time?”

“U.S. Marine Corps time. They have to get them back by nightfall, so I expect they’ll be prompt.”

The Marines were a little early, in fact. At a quarter to one, they could hear the strained throbbing of the cargo helicopters working their way around the island. They probably didn’t want to fly directly over it. Don’t annoy an armed populace.

They were two huge flying-crane cargo helicopters, each throbbing rhythmically under the strain of its load, a sand-colored Powell tank that swung underneath with the ponderous grace of a sixty-tonne pendulum. They circled out over the reef before descending to the Poseidon site, a forty-acre rhombus of sand and scrub inside a tall Hurricane fence.