After a minute’s search, it found the intake tube as well. That could come in handy. If you plugged it up, how long would it be before the reactor started to heat up and shut down? Or melt down.

It inspected the parts of the blast shield that were in reasonably deep water, not wanting to attract attention. A nine-foot-long hammerhead would be pretty conspicuous in shallow water. It could hear children splashing and swimming on the village side of the shield, and was tempted to give them something to tell their playmates about—just swim up and smile—but no, best not to do anything unusual, unsharklike.

It might be on camera, anyhow. Better act like a confused fish who just wandered in too close to shore. Hammerheads are curious and incautious.

As if in response to the thought, it heard a powerful motor roar into life and begin heading its way. It swam quickly for the depths.

Fast boat. It caught up with the changeling before it got out of the relative shallows. There was a loud bang! and a harpoon spiked completely through the shark body, just below its head.

The motor immediately throttled down, and someone began to haul in his prize. The changeling let itself be pulled halfway to the boat and then flexed a sudden 180 degrees—hammerheads are agile—and swam away at top speed.

At the end of the line there was a sudden tug; then a scream and splash. Just for fun, the changeling flexed again and sped back to the boat, only a little hampered by the harpoon. The man was still halfway in the water when the shark bumped into his foot, the immediate change in the water’s flavor a testimony to how much he enjoyed the experience.

Someone aboard the boat started firing a large pistol into the shark, two hits and two misses. The changeling twisted under the boat and took a healthy bite of fiberglass hull, and then headed at top speed for deep water. Once safely out of sight, it stopped the dramatic but unnecessary bleeding, and temporarily enlarged the first wound so that the harpoon could slide out easily. Then it swam north, staying comfortably deep.

It wondered whether the men had been motivated by fear or greed. Probably greed; with the harpoon and gun, they were set up for shark fishing. Its fins would make several thousand dollars’ worth of soup, which was why there weren’t many large sharks in the area, despite the abundance of food.

The mask, snorkle, and fins were still safe under the rock. It took only ten minutes of pain to change back into the young woman, and another thirty seconds to secrete the bathing suit material. It was an imperceptible half-inch shorter because of the loss of material to the woundings. It would catch and absorb a couple of reef fish on the way back.

It was interrupted in that simple task. It had chased and caught a large snapper, and was enlarging an orifice to absorb it, when it heard a human voice.

The ticket-taking girl was about a hundred meters away, at the edge of the reef, shouting and gesticulating. It let the snapper go and relaxed the orifice to its usual size and let the bathing suit cover it. It swam toward her as a human might, relaxed on its back, with the mask pulled up to its forehead.

“You are Mrs. Rae?” the girl said.

“Rae Archer,” the changeling said, standing up in the meter of water.

“Mr. Wade thought you were here.” The man who owned the B-and-B. “He said the project people called for you and they want you to come at eleven. It’s almost ten.”

Time flies when you’re having fun. “Thank you. I’d better hurry, then.” The changeling kept its swimming speed down to that of an athletic human and then waded ashore with convincing clumsiness, in its fins. It could have taken them off, but it knew the pebbles were too sharp for human comfort. It retrieved lavalava and sandals and jogged back to the B-and-B.

It took a cold shower and shampooed quickly, though it could have done a better job on its skin surfaces and hair just by sitting alone for twenty seconds. It put on tropical office clothes and let Mr. Wade drive “her” to Poseidon, though she could have walked and been on time.

But if she had done that and shown up not sweaty and flushed, someone might wonder.

Outside the Poseidon gate, two men had a light fishing boat up on two sawhorses, showing a crowd of gawking kids the shark bite near the bow.

A large muscular woman, Naomi, met her at the door, but instead of going inside, led her back down the road to cottage 7. They left their shoes at the door, along with two other pair, and went into the air-conditioning.

At a wooden table, a man and woman in fit middle age. The woman looked familiar. Some pieces fell into place and the changeling remembered it had graded her papers at Harvard, back in 1980.

It shook his hand, Russell Sutton, and he introduced it to its former student, Dr. Jan Dagmar. They both looked hollow-eyed and wired, as if they’d done a couple of all-nighters on pills and coffee. They sat down heavily.

“Coffee?” Naomi asked, and the changeling said yes, black, and sat down across from Jan.

“First, tell us what you know about the project,” Jan said.

“That would take a while,” the changeling said. “I’ve done my homework.” Jan shrugged in a friendly way.

It accepted the coffee. “Thanks. You stumbled onto this undersea artifact and salvaged it, and soon found that it was made of some substance too dense to find a place on the periodic table. Three times as dense as plutonium, but not radioactive.”

“Three times if it’s solid,” he said. “It’s probably hollow.”

The changeling nodded. “If it’s from Earth, it was made by some process we don’t understand—putting it mildly! Likewise, if it was made on some other planet. You still don’t know how it might have been made, but it’s intellectually less uncomfortable to assume it came from somewhere else.”

“Which is what piqued your interest,” Russ said.

“Me and seven billion others,” it said. “Ever since your announcement, my computer opens up every morning with a search for new material with the word ‘Poseidon.’ “

It sipped its coffee. “You haven’t been able to drill or file so much as a molecule off this thing. You tried to boil some off with a laser and… there was an accident.”

“You know what happened then?”

“No. I saw the CNN pictures and read the popular press speculations. The thing can levitate?”

He raised an eyebrow. “We saw the pictures, too.”

“But you haven’t published anything about it.”

“No.” He looked at Jan and back at the young woman. “We can tell you a little more if you’re hired and sign the nondisclosure form.”

“But only a little more,” Jan said. “There’s not that much to tell.”

“You got a bachelor’s in astronomy,” Russ said, “and then you quit?”

“Marriage,” the changeling said, “and when it didn’t work out, he left me with too much debt for me to go back to being a student.” This was a part of its autobiography that would stand up to computer search, but not much beyond that. The “husband” had conveniently dropped off the map, and its state and federal tax forms were precisely hacked, as were employment records for the two low-level lab technician jobs.

It had gone to some trouble to find two Los Angeles firms that were so large and mobile that Rae might credibly not be remembered personally.

“I did some checking,” Naomi said. “Your professors at Berkeley had a high opinion of you.”

The changeling gave her a level gaze. “And they wondered why I hadn’t gone on.”

“And why you became a lab tech.”

“I had the training, from summer jobs. There aren’t any jobs in astronomy.”

“That’s for sure,” Jan said. “More than half the Ph.D.s are doing something unrelated to astronomy.”

“I knew that when I chose the major,” the changeling said. “My advisor advised me to learn how to flip hamburgers.”