Laj Drai found his hired schoolteacher beside one of the torpedoes, checking off its contents with loops of one tentacle. The mechanic was listening as he named off the items.

“Magnesium cell; titanium cell; sodium — oh, hello, Drai. Anything going on?”

“Hard to say. You are setting up a research project, I take it?”

“Just checking some hypotheses. I’ve listed all the elements that would be gaseous under the conditions of Planet Three, and as many compounds as I could find in the Tables. Some are a little doubtful, since I have no pressure data; they might be liquid. Still, if they are there in any quantity, their vapors should be present.

“Then I eliminated as many as possible on theoretical grounds, since I can’t test for everything at once.”

“Theoretical grounds?”

“Yes. For example, while fluorine is still gaseous under those conditions, it’s much too active to be expected in the free state. The same is true of chlorine — which may be liquid — and oxygen. On the other hand, hydrogen seems very likely, along with hydrogen sulfide and other volatile compounds of both those elements. Nitrogen should be present, and the inert gases — though I don’t know how I can test for those.

“I’ve built little cells containing various materials, along with built-in heaters; and I’m going to warm them up one at a time after landing this torpedo and opening it to the atmosphere. Then I’ll bring it back and see what the air did to my samples. I have magnesium and titanium, which should detect the nitrogen, and sodium, and a couple of sulfides which should be reduced if there’s much hydrogen, and so on. The report may not be complete, but we should learn something.”

“So I should say, from what little I know about it Were you planning to send the torpedo out right away?”

“Yes; everything seems to be ready, unless there are complications from your department.”

“Nothing much. We were just going to send one out ourselves; our native signalled a short time ago.”

“Can you control two torpedoes at once?”

“Yes, easily. It occurs to me, however, that it might be best for you to keep a mile or two away from our homing station, and make your descent when that part of the planet is in darkness. The natives are diurnal, we are sure; and it would be a pity to scare them off if any of your chemical reactions are bright or noisy or smelly.”

“Or affect some sense we don’t know about. All right; you have a good point. Do you want me to wait until you have finished your trading, or go ahead of you if the chance occurs?”

“I don’t see that it matters much. I don’t remember whether it will be night or day there when the torpedoes arrive overhead; there’s a table for figuring it up in the office, and we’ll check before arrival time. I’d say if it was day, we’d go right down while you waited, and if it’s night you get first shot.”

“All right with me.”

“You’ll have to control from down here — there’s only one unit up in the observatory. It won’t matter, since you’ll be “working blind anyway. I’ll go up and tell them that you’re operating too — we have a relay unit with detection apparatus circling the planet now, and there’s no point in having the observers think the flatlanders are out in space.”

“Have you been getting activity from them?”

“Not much. Within the last three or four years we have picked up some radiation suspiciously like radar, but it’s all been constant frequency so far. We put quarter-wave coatings of plastic with a half-reflecting film of metal on all the torpedoes, and we haven’t had any trouble. They only use a dozen different frequencies, and we’re set up for all of them — when they change, we simply use another drone. I suppose they’ll start using two or more wave lengths in one area or maybe frequency modulation eventually, and we’ll have to get a non-reflective coating. That would be simpler anyway — only it’s more expensive. I learned that when I had the Karella coated. I wonder how we’ll get around it if they learn to pick up infra-red? The torps are enough hotter than the planet to show up like novae, when we happen to start them from the ship just outside the atmosphere.”

“Let ‘em hang in space until they cool off,” Ken and the mechanic replied in chorus. “Or send them all from here, as we’ve been doing,” added the latter. Laj Drai left without further remark.

“That fellow needs a whole scientific college,” the mechanic remarked as the door closed. “He’s so darned suspicious he’ll hire only one man at a time, and usually fires them before long.”

“Then I’m not the first?”

“You’re the first to get this far. There were a couple of others, and he got the idea they were poking into his business, so I never even found out what ideas they had. I’m no scientist, but I’m curious — let’s get this iron cigar into space before he changes his mind about letting it go.”

Ken gestured agreement, but hung back as the mechanic cut the test controller into the main outside beam circuit — two multiphase signals could be handled as easily as one on the beam, and both torpedoes would be close enough together so that one beam would suffice. The mechanic’s information was interesting; it had never occurred to him that others might have preceded him on this job. In a way, that was good — the others had presumably not been narcotics agents, or Rade would have told him. Therefore he had better protective coloration than he had supposed. Drai might even be getting used to having outsiders connected with his project.

But just what did this mechanic know? After all, he had apparently been around for some time, and Drai was certainly not afraid to talk in his presence. Perhaps he might be worked up into a really effective source of information; on the other hand, it might be dangerous to try — quite conceivably one of his minor duties was keeping a watchful eye on Sallman Ken’s behavior. He was a rather taciturn individual and Ken had not given him much attention so far.

At the moment he was all technician. He was draped over the rack in front of the control board, his tentacles resting on the various toggles and verniers, and a rising hum indicated that the tubes were warming. After a moment, he twisted a vernier knob slightly, and the torpedo on which Ken had been working lifted gently from the cradle. He spoke without turning his eyes backward:

“If you’ll go to the far end of the room, I’ll run it down there and we can test the microphone and speaker. I know you don’t plan to use them, but we might as well have them serviceable.”

Ken followed the suggestion, testing first the sound apparatus and then the various recorders and other instruments in the cargo chamber which were intended to tell whether or not any violent chemical reactions took place — photocells and pyrometers, and gas pumps connected to sample flasks and precipitators. Everything appeared in working order and was firmly clamped in place.

Assured of this, the operator guided the little vessel to a tunnel-like air lock in one wall of the room, maneuvered it in, pumped back the air, and drove the torpedo out into the vacuum of Mercury’s surface. Without further ado he sent it hurtling away from the planet, its control keyed in with a master achronic beam running from the station to the relay unit near Earth. No further attention would be needed until it approached the planet.

The mechanic rose from in front of the panel, and turned to Ken.

“I’m going to sleep for a while,” he said. “I’ll be back before arrival time. In case you care, you’ll be making the first landing. It takes one and a half revolutions of Planet Three, more or less, to get the torpedo there when the planets are in their present relative positions — we can’t use overdrive on the drones — and the signal must have come during the local daytime. I’ll see you. Have me paged if you want me for anything.”

Ken gave the equivalent of an affirmative nod.

“All right — and thanks. Your name is Allmer, isn’t it?”

“Right — Feth Allmer.” Without further speech the mechanic disappeared through the door, moving with the fluid ease of a person well accustomed to Mercury’s feeble gravity, and leaving Sallman Ken in a very thoughtful mood behind him.

Almost unconsciously the investigator settled onto the rack deserted by Allmer, and stared blankly at the indicators in front of him. One of his troubles, he reflected ruefully, was his tendency to get interested in two problems at once. In one way, that might be good, of course; the genuine absorption in the problem of Planet Three was the best possible guard against suspicion of his other job; but it didn’t help him to concentrate on that other. For hours now he had thought of practically nothing but his test project, until Allmer’s parting remarks had jarred him back to duty.

He had assumed Allmer was a competent technician, but somehow he had not expected the acuity the elderly fellow had just displayed. Ken himself had missed the implication of Drai’s statement concerning the habits of the natives of the third planet; apparently Drai had not even thought of doing his own reasoning.

But could he be that stupid? He, unlike Ken, knew the distances involved in a flight to that world, and the speed of the torpedoes; he had, on his own word, been trading here for years. What purpose could he have in trying to appear more stupid than he really was?

One possibility certainly existed. Ken might already be under suspicion, and facing a conspiracy to make him betray himself by overconfidence. Still, why in that case had the mechanic betrayed his own intelligence? Perhaps he was building himself up as a possible confidant, in case Ken were to grow communicative. If that were so, Feth was his greatest danger, since he was most in Ken’s company and in best position to serve as a spy. On the other hand, the fellow might be completely innocent even if the group as a whole were engaged in smuggling, and his recent words might have been motivated by a sincere desire to be helpful. There seemed no way of telling at the moment which of these possibilities was the more likely; Ken gave the problem up for the moment as insoluble with the data on hand.

The other problem was demanding his attention, anyway. Some of the indicators on the board in front of him were fluctuating. He had learned the panel fairly well in the last day or two, and was able to interpret the readings himself. It seemed, he noted, that pressure and temperature were both going down in the cargo chamber of the projectile. Well, that was reasonable. There were no heaters working, and the pressure would naturally drop as the gas cooled. Then it occurred to him that the temperature of Planet Three was low enough to freeze sulfur, and his test units would be covered with a crust of the stuff. Something should be done about that.

As a matter of fact, most of the pressure drop was due to leakage; the cargo door had cooled and contracted sufficiently to let air escape slowly around its edges. Ken, however, did not think of that; he found the appropriate switch and tripped it, watching the pressure drop instantly to zero as the door opened. The temperature was almost unaffected — if anything, it dropped more slowly, for the recording pyrometers were now insulated by a vacuum and the expansion of the gaseous sulfur into empty space had had no cooling effect to speak of. A touch on some of the switches which were designed to heat the test substances showed that the little furnaces were still in working order, and after a moment’s thought Ken allowed the magnesium and titanium specimens to come up to melting temperature. Then, sure that they were as free of contaminating gases as could be managed, he watched the recorders as the samples cooled again. Through all this, the torpedo hurtled on, unaffected by the extra drain on its power.

For some minutes Ken continued to wait, one eye roving over the dials and the other glancing casually about the great room; but finally he decided that Allmer had picked a good time to go off duty. He did not feel tired himself, but gradually he became convinced that there must be something a little more constructive to do. He suspected that, even if there were to be any drugs around the station, they would not have arrived yet, so there was no use making a search for them; but preparations might be made to see just what came back in the other torpedo.

As a first step, it might be well to go up to the observatory to find out just who was guiding that missile. If it were Drai himself, it would be a point in favor of Rade; if not, it would be another person from whom information might be obtained. There seemed little doubt that no one would be allowed to run the trading torpedo who did not know exactly what was being obtained on the third planet — the Planet of Ice, as Ken was coming to think of it (not that he thought of ice as a substance; he had never seen the material and would have thought of it as hydrogen oxide in any case. Planet of Solid Sulfur comes closer to the way he would have expressed the thought).

Ken was basing his supposition on his memory of how Drai had refrained from naming the substance obtained from the planet; and, determined to find at least one small brick of data to add to his edifice of information, the investigator headed up the spiral ramp toward the observatory at the station’s highest level. No one attempted to stop him on the way, though he met a couple of workers who flipped tentacles in casual recognition. The door of the observatory was not locked, as a trial push showed, and he entered, still without opposition. He was braced for a prompt request to depart, and was a little surprised when nothing at all was said. A moment later, when his eyes had become accustomed to the dimness of the big room, he realized to his chagrin that no one was there.

“No business secrets loose so far,” he muttered.

He was about to return the way he had come, when it occurred to him that he might as well make sure of that fact. There were not many places where paper work of any sort could be kept, at least at first glance; and these he rapidly covered. They were mostly cabinets built under instrument panels, and seemed to contain nothing but tables of the motions of the planets of this system. These seemed rather valueless; their most probable use would be in navigation, and Ken could not imagine anyone’s wanting to navigate anywhere in this system except to the world of Ice. They could also be used to direct the instruments, if anyone wanted to look at the planets in question; but that seemed even less helpful.

Under the beam setting controls was a small drawer which also contained two sets of numbers — again, spatial coordinates; but this time Ken froze to attention as he realized that one set at least did not refer to planets — they contained no cyclic term. The set was short, consisting of six groups of numbers containing from six to ten digits each; but he recognized them. The first identified by spectrum a beacon star; the next three were direction cosines, giving the three-dimensional bearing to another sun; the fifth gave a distance. Normally he might not have recognized or remembered the lengthy figures; but those were the coordinates of the blazing A-class sun which warmed Sarr, his home planet. The final number was another range; and beyond question it represented the distance from the present point of observation to the listed star. Ken knew enough of the standard navigational notations to be sure of that.

The other set of numbers, then, must give the direction of the same sun relative to some local set of coordinates; and not only was he ignorant of the coordinates, but the numbers were too long to remember. To copy them would be suicide, if anything more than commercial secrecy were involved. For long minutes Sallman Ken stood frozen in thought; then, abruptly, he slipped the sheet back into the drawer, closed the latter, and as quickly as was compatible with caution left the observatory. Since the information was there, it would not do for anyone to get the idea he had been there for any great length of time. It would be better if no one knew he had been there at all, but he had been seen on the way up the ramp. He proceeded to get back to his own quarters and assume an attitude of repose, though his mind still raced furiously.

He knew his distance from home. Evidently the twenty-two days of the journey to this system had not been spent in straight-line flight; the distance was only two hundred twelve parsecs. Score one for Rade; that would be an expensive business precaution, but a normal criminal one.

The direction home from this system he did not know. It did not matter too much anyway; what the Narcotics Bureau would want would be the opposite direction, on Galactic coordinates, and there would be no mathematical connection between the two except a purely arbitrary formula which would be harder to memorize than the direction itself.

Of course, the beacon listed in the stellar coordinates was probably visible from here; but could he recognize it with any certainty without instruments? The instruments were available, of course, but it might not be wise to be caught using them. No, orientation was definitely the last job to be accomplished in his present location. At any rate, one fact had been learned and one point of probability had been added to the Rade theory. Sallman Ken decided that made a good day’s work, and allowed himself to relax on the strength of it.