The light, impotent after penetrating fifty fathoms of Tridentian sea, was murky and green-tinted; but Tom Harris had become more or less used to that. It rankled, nevertheless, that the sea-people continued to ignore his demands for a lamp.

He knew that they used such devices. Through the clear walls of his tank, he had seen night parties swimming out to hunt small varieties of fish. The water craft they piloted on longer trips and up to the surface were also equipped with lights powered by some sort of battery. It infuriated Harris to be forced arbitrarily to exist isolated in the dimness of the ocean bottom day or the complete blackness of night.

He rose from the spot where he had been squatting on his heels. So smooth was the glassy footing that he slipped and almost fell headlong. He regained his balance and looked about.

The tank was about ten by ten feet and twice as long, with metal angles which he assumed to be aluminum securing all edges. These formed the outer corners, so that he could see the gaskets inside them that made the tank water-tight. The sea-people, he had to admit, were quite capable of coping with their environment and understanding his.

The end of the tank distant from Harris was opaque. He thought that there were connections to a towing vehicle as well as to the plant that pumped air for him. The big fish had not made that quite clear to him. All other sides of the tank were quite clear. Whenever he walked about, he could look through the floor and find groups of shells and other remnants of deceased marine life in the white sand. Occasionally, he considered the pressure that would implode upon him should anything happen to rupture the walls, but he had become habitually successful in forcing that idea to the back of his mind.

Along each of the side walls were four little airlocks. The use of these was at the moment being demonstrated by one of the sea-people to what Harris was beginning to think of as a child.

The parent was slightly smaller than Harris, who stood five-feet-five and weighed a hundred and thirty pounds Terran. It also had four limbs, but that was about the last point they had in common. The Tridentian's limbs all joined his armored body near the head. Two of them ended in powerful pincers; the others forked into several delicate tentacles. The body was somewhat flexible despite the weight of rugged shell segments, and tapered to a spread tail upon which the crustacean balanced himself easily.

Harris felt at a distinct disadvantage in the vision department: each of the Tridentians had four eyes protruding from his chitinous head. The adult had grown one pair of eye-stalks to a length of nearly a foot. The second pair, like both of the youngster's, extended only a few inches.

The Terran could not be sure whether the undersea currency consisted of metal or shell, but the Tridentian deposited some sort of coin in a slot machine outside one of the little airlocks. It caused a grinding noise. Directly afterward, a small lump of compressed fish, boned, was ejected from an opening on the inside.

"Goddam' blue lobsters!" swore Harris. "Think they're doing me a favor!"

He let them wait a good five minutes before he decided that the prudent course was to accept the offering. Sneering, he walked over and picked up the food. There was usually little else provided. On days he had been too angry or too disgusted to accept the favors of sightseers, his keepers assumed that he was not hungry.

In the beginning, he had also had a most difficult time getting through to them his need for fresh water. That was when he had come to believe in the large, fish-like swimmer who had transmitted his thoughts to the sea-people. The fact that the latter could and did produce fresh water for him aroused his grudging respect, even though the taste was nothing to take lightly.

He juggled the lump of fish in one hand, causing the little Tridentian to twirl his eye-stalks in glee and swim up off the ocean bottom to look down through the top of the tank. The parent also wiggled his eye-stalks, more sedately. Harris suspected them of laughing, and turned his back.

Looking through the other side of his tank, he could see—to such distance as the murky light permitted—the parked vehicles of the Tridentians. Like a collection of small boats, they were of sundry sizes and shapes, depending perhaps upon each owner's fancy, perhaps on his skill. Harris did not know whether the Tridentians' craftsmanship extended to the level of having professional builders. At any rate, they were spread out like a small city. Among them were tent-like arrangements of nets to keep out swimming vermin. Other than that, the sea-people used no shelters.

They were smart enough to build a cage for me! he thought bitterly. What the hell is the matter with the Terran government, anyway? That Department of Interstellar Relations, or whatever they call it. Why can't they get me out of here? And where did Big Fish go now?

He saw several of the crustacean people approaching from the camping area. Shortly, no doubt, he would again be a center of mass attention, with cubes of compressed and stinking fish shooting at him from all the little airlocks. He snarled wordlessly.

The groups seemed to come at certain periods which he had been unable to define. He could only guess that they had choice times for hunting besides other work that had to be done to maintain the campsite and their jet-propelled craft.

I'd like to get one of them in here and boil him! thought Harris. Big Fish claims they don't taste good. I wonder. Anyway, it would shake them up!

He had long since given up thinking about what the sea-people could do to him if they chose. Their flushing the tank eighteen inches deep with sea water twice a day had soon given him an idea, especially as he had nowhere to go during the process. He no longer permitted himself to fall asleep anywhere near the inlet pipe.

He noticed that the dozen or so sightseers were edging around the end of the tank to join the first individual and his offspring. Looking up, Harris saw the reason. A long, dark shadow was curving down in an insolently deliberate dive. It was streamlined as a Terran shark and as long as the tank in which Harris lived. The flat line of its leading edge split into something very like a yawn, displaying astonishing upper and lower carpets of conical teeth. This was possible because the eyes, about eight Harris thought, were spaced in a ring about the head end of the long body.

They know I don't like to eat them, but I like to scare them a little. Big Fish thought to Harris. Look at them trying to smile at me!

Harris watched the Tridentians wiggling and waving their eye-stalks as the monster passed lazily over them and turned to come slowly back.

"I'd like to scare them a lot," said Harris, who had learned some time ago that he got through better just by forgetting telepathy and verbalizing. "Is the D.I.R. man still there?"

Which ... what you thought? inquired Big Fish.

"The other Terran, the one on the island."

The other air-breathing one is gone, the other Big Fish is feeding, as I have done just now, and it is not clear about the far Terran who lacks a Big Fish.

"All the bastards on both worlds are out to lunch," growled Harris, "and here I sit!"

You are in to lunch, agreed the monster.

The three eyes that bore upon the imprisoned man as the thinker swept past the tank had an intelligent alertness. Harris had come to imagine that he could detect expressions on Big Fish's limited features.

"You're the only friend I've got!" he exclaimed, slipping suddenly into self-pity. "I wish I could go with you."

Once you could, when you had your own tank.

"It was what we call a submarine," said Harris. "I was looking to see what was on the ocean floor. Tell me, is it all like this?"

Is it all like what? With blue lobsters?

Harris still retained enough sanity to realize that the Tridentians did not suggest Terran lobsters to this being who probably could not even imagine them. That was an automatic translation of thought furnished out of his own memory and name-calling.

"No," he said. "I mean is it all sand and mud with a few chasms here and there? Where do these crabs get their metals?"

There are different kinds of holes and hills. It is all mostly the same. You cannot swim in it anywhere, although there are little things that dig under the soft sand. Some of them are good to eat but you have to spit out a lot of sand. The crabs dig with machines sometimes, in big holes, but what they catch I do not know.

"Isn't there anything that catches them?" asked Harris bitterly.

No. They are big enough to catch other things, except a few. Things that are bigger than I am are not smart.

The monster made a pass along the ocean bed near the Tridentians, stirring up a cloud of sand and causing Harris's captor to shrink against the side of his tank. The Terran laughed heartily. He clapped the backs of his fists against his forehead above the eyes and wiggled his forefingers at the Tridentians on the other side of the clear barrier.

Even after the sand had settled, he ran back and forth along the side of his tank, making sure that every sightseer had opportunity to note his gesture. He had an idea that they did not like it much.

They do not like it at all, thought Big Fish. Some of them are asking for the man who lets the sea into your tank.

"Don't call it a man!" objected Harris, giving up his posturing. "I am a man."

What else can I call these men except men? asked the other. I do not understand why you want to be called a man. You are different.

"Forget it," said Harris. "It was just a figure of thought."

He felt like sitting down again, but decided against it in case the onlookers should succeed in obtaining the services of the tank attendant. He walked to the end of the tank, where he could stare into the greenish distance without looking at the Tridentian camp.

"I wish I were dead," he muttered. "They'll never get me out of here."

Behind him, he heard the plop-plop of food tidbits landing on the floor of the tank as the onlookers sought to regain his attention. They must have come out of their moment of pique if they were trying to coax him to amuse them further.

"If I could find a bone in those hunks of fish, I'd kill myself," said Harris.

The dark shape of Big Fish settled over the tank, cutting off what little light there was like a cloud. Harris looked up resentfully.

I do not understand you, thought the monster. That would be very foolish.

"What—trying to commit suicide with a fish bone?"

No matter how, it would be extremely foolish, for then you would be dead.

Harris could not think of anything to say. He could not even think of anything to think, obviously, since none of his chaotic, half-formed thoughts brought a response.

It would be as if you had been eaten, insisted his friend.

"All right, all right! I won't do it then, if that'll make you happy," exclaimed Harris.

It has no effect on how well I feed, Big Fish informed him.

It took Harris a minute, but he figured it out.

"So that's your philosophy!" he muttered to himself. "Now I know what it takes to make you happy. Something to eat!"

Where? inquired the monster. I do not see anyone I want to eat.

"Never mind!" said Harris. "Tell me more about the ocean bottom. Where there are big holes or cliffs, can you see ... uh ... stripes in the sides, layers of rock?"

Sometimes. Where it is deep enough. Other places there are things growing to the bottom. Only little fish that are not even good to eat do their feeding there. Sometimes the sea-people take away the growing things or dig holes.

"I'll bet there are plenty of things to get out of this ocean," mused Harris. "Who knows how the climate may have changed in thousands of years. Maybe if there was an ice age the seas would have shrunk. Maybe there was a volcanic age. Maybe you could drill underwater and find oil—if you knew where to look. Maybe there are deposits of diamonds under the ooze."

He stopped when he sensed a vague irritation. He realized that his thoughts had been going out and scoring the cleanest of misses.

"It doesn't matter," he said. "Just tell me what you do know about the sea."

I can tell you where to find tribes of the sea-people. I can tell you where to find all sorts of good eating-fish. I know where to think to other Big Fish but that I cannot tell you, for you cannot feel it.

The monster rose slowly through the water. He had seen something up there that interested him, Harris knew, and would return when it occurred to him.

He considered the possibilities. Perhaps there was something in the idea of building up a food industry. If you had inside tips on where the fish were, how could you miss? Then, the Tridentians must have some knowledge of where to find metals, since they used them. He suspected that they had factories somewhere.

"Come to think of it," he asked himself, "how do I know it isn't some savage tribe that picked me up? One of these days, I may wind up with a more advanced bunch. I'll have to ask Big Fish when he comes back."

He began to plan what he would do if he reached some higher civilization under the sea. Anyone with the knowledge to mine metals, or maybe to extract them from sea water, would be interested in contacting Terrans from another world. There would be a little trouble, probably, in getting them to comprehend space, but some of them could be sent up to the surface in tanks. Then there would be a need for some Terran who knew both worlds.

"I could wind up an ambassador!" Harris told himself. "I wonder ... maybe I could even work it with this bunch. If I could only get out of here! Come back in another submarine, maybe."

He began to pace the length of his tank and back, stopping once to gather up the fish that had been bought for him by some of the crowd outside. He noted that the latter was constantly changing without varying much in total number. He took to walking around the sides of the tank, staring into each set of eyes.

In the end, this had such a hypnotic effect that he imagined himself swimming through the dim, greenish light. The sea-people outside began to appear as individuals. He grew into the feeling that he could recognize one from the other.

He found himself running for the corner where he had collected his fish. The sound that had triggered the reaction originated at the opaque end of the tank. It was followed within seconds by several jets of water, white and forceful, which entered near the floor of the structure.

Harris snatched up his supply of food to keep it from being washed away. With one hand, he tried to roll up the legs of his pants. He never seemed to be prepared when the time came, but he was constantly too chilled to go around with the trousers rolled up all the time.

The water swished about the calves of his legs. After a few minutes, it began to recede as the Tridentian machinery pumped it out. Soon, the tank was clean of everything but Harris, his fish, and the thick smell of sea water.

He was good, came a thought. I see you are eating too.

A large shadow passed overhead. Most of the Tridentians wiggled their eye-stalks in an effort to look amiable. Harris dropped his fish to the damp floor.

"No, I'm not eating," he said. "I'm all wet."

So am I, answered Big Fish.

"But I'm not usually," said Harris.

I know. It is unkind, they way they let you dry out. Would you like me to knock in the end of the tank? You could have all the water you want.

"Not right now," said Harris calmly. He sat down, crossing his legs. "I'll have to grow some gills first. It may not take much longer, at that."

He looked at the Tridentians, who looked in at him. Again, he felt the sensation of being able to recognize individuals. Perhaps he should talk to them more often through Big Fish.

"Maybe some of them are really nice fellows," he muttered, "if I just get to know them better."

No, his friend told him, they are not very good to eat.