I obeyed. I had a little trouble; the garment wasn’t as simple as it looked. One of the buckles proved to have a sharp corner which cut quite a deep gash on my hand and I wondered what sort of quality control would put up with that sort of design. The drops of blood looked a little strange, bright-red globules rising from the wound, but the injury was minor. By the time Bert had solved my problem with the buckle the bleeding had stopped.

He checked my coverall, especially the wrist and helmet junctions, very carefully. The others had also dressed and were doing the same for each other. Gestures which even I could interpret signified that the checks were complete, and Bert turned to the door.

He manipulated a dial at its side, and the great valve — large enough to accommodate a small work sub — swung easily open. He waved us through, waited until we had passed and closed the portal behind us. It struck me again that his air was not merely one of familiarity but of authority. How, in a single year, could a Board agent have made himself so completely trusted by these people? A Board agent, of all people on Earth the most likely to take action against them and their way of life? Gould he have been in contact with them even before his disappearance from the surface a year ago? Could Marie be right? And if she were, what was I getting into? I had trusted Bert Whelstrahl completely when I first saw him down here and had tossed off most of Marie’s claims as coming from a woman nearly hysterical with grief; it had seemed likely enough that her Joey — not that he’d ever been hers, in his own estimation — had actually never reached this place. Enough other things could happen to make a one-man sub disappear in the Pacific.

Now I was wondering, deeply. But there were other matters claiming attention.

For the first time, I found myself in a tunnel which was obviously slanted steeply — the pull of my ballast belt let me judge ‘up” and ‘down” easily enough when I paid attention to the matter. We were heading downward at fully sixty degrees. The tunnel lights, the only distinct features on the walls, were going by at a speed which showed we were being helped by pumps; there was certainly a downward current. I wondered if we’d have to swim against it on the way back and decided it wouldn’t be possible. Either they’d reverse the flow, or we’d use another tunnel.

I didn’t notice any temperature change, though I knew we were going to examine a heat engine. Maybe this bunch was moral enough about energy waste when it came to the sort of leakage which robbed a machine of efficiency, no matter how they behaved about it afterward.

I couldn’t guess how far down we went before reaching the control chamber. It was certainly hundreds of feet, probably thousands, possibly as much as a mile. I did see the charts of the layout later on, but the peculiar ideas of scale used by their makers still defeats me. It was certainly far enough down to present a hopeless obstacle to any brute-force defense against pressure as armor.

The room itself was big enough to make the far end hard to see. The liquid, as I guess I may have forgotten to mention, scattered light just a trifle and gave objects more than fifty yards or so away a foggy appearance.

The room, though, as a control chamber was almost shockingly conventional. It contained along one wall a pattern of lines which even I could recognize as a distribution net. Below this was another pattern, harder to recognize but of noticeably vertical orientation, and I suspected that it indicated the working-fluid circuits between the heat source far below and the converters and heat sink at the top. A heat engine of any sort works on pretty basic thermodynamics, and its diagrams are apt to resemble those of its relatives whether it’s a steam turbine or a thermocouple.

Along the lines of both diagrams were indicators, mostly of familiar dial-and-needle type, switches and rheostats. Nothing was mystifying; it was a power plant control at a glance. That is, it could be recognized at a glance. It could be learned, given luck and competence, in a month or two.

Thirty or forty swimmers, suited and helmeted like ourselves, drifted a few feet from the control wall, all their attention focused on it. This was a little surprising. I would have expected fewer operators on a board of this size. If they were all necessary for manual control, it was another mark against the general level of technical competence here, like the sharp buckle. I hoped that — poor coordination on their part would merely result in nuisance rather than catastrophe. No doubt there were fail-safe breakers in the electric distribution net and some sort of emergency bleed-offs here and there in the fluid lines, but even so that crowd of operators gave a certain primitive air to the whole thing. I watched thoughtfully. The ones who had come in with us looked with as much interest as I felt; I got the impression that they hadn’t been here before either. Well, that was quite possible. The whole population could hardly be composed of power engineers.

It added to the mystery, though, because I knew that Bert wasn’t one either. He had a general engineering background like my own, which of course you need to be any good at tracking down power waste. Why should he have authority around here?

He turned and made a couple of gestures at our escort. Then he wrote me a message.

“Don’t get close enough to distract any of these people. More than half of them are trainees.” That put a slightly better light on the situation.

“You take your education here seriously,” I answered.

“You bet we do. You’ll see why, soon. Swim around as much as you want and look at what you want — you know enough so I don’t have to watch you like these others. Just don’t get in front of an operator.”

I nodded. For the next half hour I did just as he had written, examining the entire board in as much detail as I could. The arrangement made more and more sense as time went on. One very surprising reason for this was that the dials and control knobs were marked in perfectly ordinary numbers. I hadn’t expected that, after seeing what seemed to pass for writing down here.

The numbers were alone, unfortunately — no units such as volts or megabars were given. In spite of this, the position of each instrument on the diagram which formed the board usually gave a pretty good clue to its purpose. In less than an hour I felt I understood the system pretty well.

Ten shafts led down to the heat absorbers at the source — presumably a magma pocket. The details of the absorbers themselves weren’t obvious from the board, but I knew enough about volcanic installations to guess. I’d done a waste investigation in Java once. The working fluid was water; the still which took in sea water and desalted it, the electrolysis units which got alkali metals from the recovered salts, and the ion injection feeds were all obvious on the board.

The MHD converters were also ten in number, but all exhausted into a common condenser which appeared to be cooled by outside sea water. It did not serve as a preheater for the still, which seemed wasteful to me. Without units on the gauges I couldn’t be sure of the net power developed, but it seemed obvious that it had to be in megawatts at least.

I hadn’t noticed the sound of which Bert had warned, but perhaps that was because of the suit. I took a chance and loosened slightly one of the cuffs between sleeve and glove. There was sound, a heavy drone like a vast organ pipe and no doubt due to the same physical cause. It wasn’t painful, but I could tell that removing the protecting suit entirely might be unwise. I wondered how close we actually were to the steam tunnels which must be the source of the hum. Even more, I wondered about their maintenance, but I had to do without details for the time being.