"A smart person keeps his bike tightened up," remarked the youngster who had spoken before.

"Quite right," Bob agreed, paying no more attention to him. "I'm OK, Mae. See you later." He remounted the machine and started down to the road, not looking back this time.

"Shouldn't you tighten it up?" the Hunter asked, "We have tools, don't we?"

"Sure, in the case," was the reply. "It isn't loose, though."

"But-" The Hunter stopped talking as his mind drew too far ahead of his words.

"Yeah. But. We'll think it over later on." There was no time for more conversation, even if there had been thought to feed it. The journey to the Seevers' was short, and they had already arrived.

Jenny met them at the door. If she had been unhappy about anything when she had left them, there was no sign of it now.

"Come on in," she said cheerfully." Dad's in the office, and we have something to show you." She led the way.

"Seever was sitting at his desk, examining with interest an open box about a foot square and half as deep. It was made of thin wood, with the seams heavily caulked and a gasket on the rim where the lid presumably was sealed. Clearly it was meant to be watertight. It contained a quantity of obviously electrical equipment-coils, batteries, and vacuum tubes -which told both the newcomers what it must be though the details were far from clear. Bob had of course taken several physics courses on his way to the chemical engineering degree, and the Hunter had paid some attention to both, reading and lectures, but neither had more than the roughest idea how a metal-detector worked.

"That was a quick job!" Bob exclaimed. Seever answered.

"Not exactly. It was made long ago, well before your father asked for it. Tavake's kids have been using it for months. The only reason he didn't hand it over when Arthur asked for it yesterday was that the young ones were out using it. Taro was surprised when Jenny came around today asking for the same thing. He only gave it to her when she explained it was the same project and would get to the same people."

"The word's spreading like a tank leak on the lagoon," growled Bob.

"Oh, no," insisted Jenny. "Mr. Tavake doesn't know what the project is all about. I certainly didn't tell him, and I'm sure your father didn't."

"He certainly knows that something involving several people and his metal-detector is going on. In a place the size of Ell that may not be quite the same as knowing what it is, but it's the same as having every-one know that much-and the identities of the people involved. Well,I suppose it can't be helped. But if we have to ask for anything else, let's have just one person do the asking from now on."

"Did you tell Maeta?" asked Jenny.

"No, of course not. But she has to know there's something funny-"

"Well with that slip of yours about 'they must be here', she probably won't ask me what I know, but she'll be asking me whether I know anything. What do I tell her? You were being all pure about lying yesterday, most of the time."

"Tell her the truth, of course," snapped Bob. "That you know, but it isn't your secret." Bob was looking at Jenny as he spoke, and the Hunter regretted not being able to see the doctor's expression. It would have been nice to be able to guess his reaction to the intimation that his daughter was not always truthful. His voice cut in, but by the time Bob looked toward him he was well on his way with another matter, and the expression was probably irrelevant to the earlier question.

"Please let me know what you do tell her, Daughter. Maeta works here sometimes, remember, and I don't want to make any slips talking to her because of what she has or hasn't been told. Personally I think she's a very bright young lady who could be a big help to us, but I understand how Bob feels about letting the word spread any farther."

"I knew it," sighed Bob. "Who else, while you're at it?"

"I wasn't making a serious plea about Maeta, Bob, but I did mention Jenny's mother earlier."

"I thought I'd okayed that"

"You weren't really clear, and I didn't want to take a chance until you were."

"Well, tell her. But let's keep it in the families for a while. Of course, if I get so I can't run things, you're the boss and can do what you think best. Now, how does this metal-detector work?"

"You turn it on here. If the earphones whistle, turn the knob here until it just stops. Then if it comes close to metal, the whistle starts again. If you don't get a whistle at any knob position, put in a new battery. If that doesn't work, take it back to Taro. Nothing to it."

Bob picked up the box. "It's much too light to sink.

How do we ballast it for underwater use?"

Seever pointed to a larger box made of concrete, on the floor beside his desk. What looked like a lid lay next to it. Four eyebolts projected from the sides of the cube, as did an insulated wire; it looked as though the concrete had been poured around these.

Seever's explanation corrected one point; the "lid" was actually the floor of the device. The wooden box was supported well above this, and trapped air would keep any water which leaked in well below the electrical equipment, at least to any reasonable depth, as long as everything was kept upright.

"Taro says it's worked fine for his youngsters," Seever finished. "He's had no trouble with leaks, and they've found a lot of stuff like dropped tools on the bottom around the dock and the tanks. It sounds off for a pair of pliers at five or six feet when it's really at it's best.

"Now, Bob, tell me if I have everything straight. Jenny says you are now quite sure that the Hunter's people have been on Earth, and on Ell." Bob nodded emphatically.

"Right," he answered. "They found the generator shield, apparently read its lettering carefully, which the Hunter says would have let them identify his quarry's ship, and for some reason neither of us has been able to guess so far they moved the shield from Apu into the lagoon a mile or so, where Maeta found it. This happened several years ago, but the Hunter is certain, they wouldn't have left Earth, at least not for good. They may, he admits, have spread out from the island either to look for him and his quarry because they couldn't find them here, or to check up on the people of Earth, or both.. He is certain they would come back from time to time to check on the ship which they probably found, or both of them which they may have found. All we have to do is find at least one of themourselves and leave a message with it."

"Two questions," Seever spoke slowly, choosing his words carefully. "First, why would they have moved the shield? It seems to me you're passing over that question very casually, and you admit you haven't an answer. Second, why do you have to find the ships, or one of them, to leave a message? I could see it as a problem when your friends might have been anywhere on Earth, but you now seem sure they're on Ell at least some of the time, why not paint a message un-obtrusively under the dock?"

Bob sighed. "The second answer is the same as it always was. We still have to avoid attracting human attention. A message with any usable detail will be regular and complex enough to get not just attention but real curiosity. Both the Hunter and I feel we can't afford that. For the other point, granted it may be important but we don't see how it can affect our plans. We'd love to figure out the answer, or have someone ' else come up with a convincing one. Until someone does, we'll have to wonder."

The doctor was silent for at least a minute. "I still don't like it," he said last. "I was hoping the Hunter might recognize it as some sort of standard procedure with his police. Maybe it's not important, but I don't like jigsaw puzzles with big gaps in them, especially when there are no pieces lying around. However, we'll have to live with the situation, I guess. You really can't think of a reason, Hunter?"