"What is it?" Dalgard asked his question as Sssuri, his attention still on their back trail, stole along cautiously on a retracing of their path.

But that retreat ended abruptly with the merman plastered against the wall, his whole shadowy form a tense warning which stopped Dalgard short. In that moment the answer flashed from mind to mind.

"There are those which follow—"

"Snake-devils? Those Others?" The colony scout supplied the only two explanations he had, sending his own thought out questing. But as usual he could not hope to equal the more sensitive merman whose race had always used that form of communication.

"Those who have long haunted the darkness," was the only reply he could get.

But Sssuri's actions were far more indicative of danger. For the merman turned and caught at Dalgard, pulling the larger colonist along a step or two with the urgency of his grip.

"We cannot return this way—and we must travel fast!"

For Sssuri who would face and had faced up to a snake-devil with a spear his sole weapon, this timidity was new. Dalgard was wise enough to accept his verdict of the wisdom of flight. Together they ran along the underground corridor, soon putting a mile between them and the point where the merman had first taken alarm.

"From what do we flee?" As the merman began to slacken pace, Dalgard sent that query.

"There are those who live in this darkness. By one, or by two, we could speedily remove them from life. But they hunt in packs and they are as greedy for the kill as are the snake-devils scenting meat. Also they are intelligent. Once, long before the days of burning, they served Those Others as hunters of game. And Those Others tried to make them ever more intelligent and crafty so they might be sent to hunt without a huntsman. At last they grew too knowing for their masters. Then Those Others, realizing their menace, tried to kill them all with traps and tricks. But only the most stupid and the slowest were so disposed of. The others withdrew into underground ways such as this, venturing forth only in the dark of night."

"But if they are intelligent," countered the scout, "why can they not be reached by the mind touch?"

"Through the years they have developed their own ways of thought. And these are not the simple creatures of the sun, or such as the runners. Once they were taught to answer only to Those Others. Now they answer only to each other. But"—he spread out his hands in one of his quick, nervous gestures—"to those who are cornered by one of their packs, they are sudden death!"

Since they could not, by Sssuri's reckoning, turn back, there was only one course before them, to follow the passage they had chanced upon. The merman was certain that it underran the river and that eventually they would reach the sea—unless some side turn before that point would make them free in the countryside once more.

Dalgard doubted if it had ever been a well-used way. And the presence of earth falls here and there, over which they stumbled and clawed their way, led him to consider the wisdom of keeping on to what might be a dead end. But his trust in Sssuri's judgment was great, and as the merman plowed forward with every appearance of confidence, he continued to trot along without complaint.

They snatched moments of rest, taking turns at guard. But the walls about them were so unchanging that it was hard to measure time or distance. Dalgard chewed at his emergency rations, a block of dried meat and fruit pounded together to an almost rocklike consistency, and tried to make the crumbs he sucked loose satisfy his growing hunger.

The passageway was growing damper; water trickled down the walls and gathered in fetid pools on the floor. Dalgard's dislike of the place grew. His shoulders hunched involuntarily as he strode along, for his imagination pictured the rock above them giving away to dump tons of the oily river water down to engulf them. But though Sssuri avoided splashing through the pools wherever he might, he did not appear to find anything upsetting about the moisture.

At last the human could stand it no longer. "How much farther to the sea?" he asked without any hope of a real answer.

As he had expected him to do, Sssuri shrugged. "We should be close. But having never trod this way before, how can I tell you?"

Once more they rested, choosing a stretch which was reasonably dry, munching their dried food and drinking sparingly from the stoppered duocorn horns which swung from their belts. A man would have to be dying of thirst, Dalgard thought, before he would palm up any of the stagnant water from the passage pools.

He drifted off into a troubled sleep in which he fled beneath a sky which was a giant lid in the hand of an unseen enemy, a lid which was slowly lowered to crush him flat. He awoke with a start to find Sssuri's cool, scaled fingers stroking his shoulder.

"Dream demons walk these roads." The words drifted into his half-awake mind.

"They do indeed," he roused to answer.

"It is always so where Those Others have been. They leave behind them the thoughts which breed such dreams to trouble the sleep of those who are not of their kind. Let us go. I would like to be out of this place under the clean sky, where no ancient wickedness hangs to poison the air and thought."

Either the merman had miscalculated the direction of their route or the river mouth was much farther from the inland city than they had believed, for, though they pushed on for what seemed like weary hours, they came to no upward slope, no exit to the world they knew.

Instead Dalgard began to realize that just the opposite was true. At last he could stand it no longer and broke out with what he feared, hoping that Sssuri would deny that fear.

"We are going downhill!"

To his disappointment the merman agreed. "It has been so for the last thousand of our paces. It is my belief that this leads not to the sun but out under the sea."

Dalgard missed a step. To Sssuri the sea was home and perhaps the thought of being under its floor was not disturbing. The land-born human was not so prepared. If he had experienced discomfort under the river, what would it be like under the ocean? His terrifying dream of a lid being pressed down upon him flashed back into his mind. But his companion was continuing:

"There will be doors, perhaps into the sea itself."

"For you," Dalgard pointed out, "but I am no dweller in the depths."

"Neither were Those Others, yet they used these ways. And I tell you"—in his earnestness the merman laid his hand once more on Dalgard's arm—"to turn back now is out of the question. The death which haunts the darkness is still sniffing out our trail."

Dalgard glanced involuntarily over his shoulder. By the faint and limited light of the purple disks he could see little or nothing. An army might creep there undetected.

"But—" His protest was in answer to the merman's seeming unconcern.

Sssuri at the first intimation that the hunters were behind them had shown wariness. Now he did not appear to care.

"They had fed," he replied. "Scouts follow because we are something new and thus suspect. When hunger rises once more in them, and their scouts report that we are meat, then is the time to draw knives and prepare for battle. But before that hour we may have won free. Let us search for the gate we now need."

However confident the merman might be, Dalgard could not match that confidence. In the open air he would have faced a snake-devil four times his size without any more emotion than a hunter's instinctive caution. But here in the dark, unable to rid himself of the belief that thousands of tons of sea water hung over his head, he found himself starting at any sound, his knife bare and ready in his sweating hand.

He noted that Sssuri had stepped up the pace, passing into his sure-footed glide which made Dalgard exert himself to keep up. Before them the corridor stretched without a break. The merman's promised exit, if it existed, was still out of sight.

It was difficult to gauge time in this dark hall, but Dalgard thought that they were at least an hour farther on their way when Sssuri paused abruptly once more, his head cocked in a listening attitude, as if he caught some whisper of sound too rarefied for his human companion.

"Now—" the thought hissed as if he spat the words, "they hunger—and they hunt!"

He bounded forward with a spurt, which Dalgard copied, and they ran lightly, the dust undisturbed in years puffing up beneath the merman's bare, scaled feet and Dalgard's hide boots. Still the unbroken walls, the feeble patches of violet in the ceiling. But no exit. And what good would any exit do him, Dalgard thought, if it opened under the sea?

"There are islands off the coast—many islands—" Sssuri caught him up. "It is in my mind that we shall find our door on one of those. But—run now, knife brother, for those at our heels awake and thirst for flesh and blood. They have decided that we are not to be feared but may be run down for their pleasure."

Dalgard weighed his knife in his hand. "They shall find us with fangs," he promised grimly.

"It will be better if they do not find us at all," returned Sssuri.

A burning arch of pain encased Dalgard's lower ribs, and his breath came in gusts of hastily sucked air as their flight kept on, down the endless corridor. Sssuri was also showing signs of the grueling pace, his round head bent forward, his furred legs pumping as if only his iron will kept them moving. And the determination which kept him going was communicated to the scout as a graver warning than any thought message of fear.

They were passing under one of the infrequent violet lights when Dalgard got something else—a mental thrust so quick and sharp it was as if a sword had cut through the daze of fatigue to reach his brain. Yet that had not come from Sssuri, for it was totally alien, wavering on a band so near the extreme edge of his consciousness that it pricked, receded, and pricked again as a needle might.

This was no message of fear or warning, but of implacable stubbornness and ravening hunger. And in that instant Dalgard knew that it came from what was sniffing out their trail, and he no longer wondered that the hunters were immune to other mental contact. One could not reason with—that!

He spurted forward, matching the merman's acceleration of speed. But to Dalgard's horror he saw that his companion now ran with one hand brushing along the wall, as if he needed that support.

"Sssuri!"

His thought met a wall of concentration through which he could not break. In a way he was reassured—for a moment, until another of those stabs from their pursuers struck him. He longed to look back, to see what hunted them. But he dared not break stride to do that.

"Ahhhh!" The welcoming cry from Sssuri brought his attention back to his companion as the merman broke into a wild run.

Dalgard summoned up his last rags of energy and coursed after him. Sssuri had halted before a dark lump which protruded from the side of the corridor.

"A sea lock!" Sssuri's claws were clicking over the surface of the hatch, seeking the secret of its latch.

Panting, Dalgard leaned against the opposite wall. Just as a protest formed in his mind he heard something else, the pad of feet, many feet, echoing down the corridor. And somehow he was able now to look.

Round spots of light, dull, greenish, close to the ground, as if someone had flung a handful of phosphorescence into the dark. But this was no phosphorescence! Eyes! Eyes—he tried to count and knew it was impossible to so reckon the number of the pack that ran mute but ready. Nor could he distinguish more than a very shadowy glimpse of forms which glided close to the ground with an unpleasant sinuosity.

"Ahhhhh!" Again Sssuri's paean of triumph.

There was the grate of unwilling metal forced to move, a puff of air redolent with the sea striking their bodies in chill threat, the brightness of violet light stepped up to a point far beyond the lamps in the corridor.

With it came no rush of drowning water as Dalgard had half expected, and when the merman clambered through the hatch he prepared to follow, well aware that the eyes, and the pattering feet which bore them, were now almost within range.

There was a snarl from the passage, and a black thing sprang at the scout. Without clear sight of what he was fighting, he struck down with his knife and felt it slit flesh. The snarl was a scream of rage as the creature twisted in midair for a second try at him. In that instant Sssuri, leaning halfway out of the hatch, struck in his turn, thrusting his bone knife into shadows which now boiled with life.

Dalgard leaped for the lock door, kicking out swiftly and feeling the toe of his boot contact with a crunch against one of those darting shades, sending it back end over end into the press where its fellows turned snapping upon it. Then Sssuri grabbed at him, bringing him in, and together they slammed the hatch, feeling it shake with the shock of thudding bodies as the pack outside went mad in their frustration.

While the merman fastened the locking bar, bringing out of the long-motionless metal another protesting screech, Dalgard had a chance to look about him. They were in a room some eight or nine feet long, the violet light showing up well tangles of equipment hanging from pegs on the walls, a pile of small cylinders on the floor. At the far end of the chamber was another hatch door, locked with the same type of bar as Sssuri had just lowered to seal the inner one. The merman nodded to it.

"The sea—"

Dalgard slid his knife back into its sheath. So the sea lay beyond. He did not welcome the thought of passing through that door. Like all of his race he could swim—perhaps his feats in the water would have astonished the men of the planet from which his tribe had emigrated. But unlike the mermen, he was not sea-born, nor equipped by nature with a secondary breathing apparatus to make him as free in the world of water as he was on land. Sssuri might crawl through that hatch without fear. For Dalgard it was as big a test as to turn and face what now raged in the corridor on the inner side.

"There is no hope that they will go now," Sssuri answered his vague question. "They are stubborn. And hours—or even days—will mean nothing. Also they can leave a guard there and rove at will, to return upon signal. That is their way."

This left only the sea door. Sssuri padded across the chamber and reached up to free one of the strange objects dangling from the wall pegs. Like all things made of the marvelous substance used by Those Others for any article which might be exposed to the elements, it seemed as perfect as on the day it had first been hung there, though that date might be a hundred or more Astran years earlier. The merman uncoiled a length of thin, flexible piping which joined a two-foot canister with a flat piece of metallic fabric.

"Those Others could not breathe under the water, as you cannot," he explained as he worked deftly and swiftly. "Within my own memory we have trapped their scouts wearing aids such as these so that they might spy upon our safe places. But their last foray was some years ago and at that time we taught them such a lesson that they have not dared to return. Since they are not unlike you in body and since you breathe the same air aboveground, there is no reason why this should not take you out of here."

Dalgard accepted the apparatus. A couple of elastic metal bands fastened the canister to the chest of the wearer. The fabric molded into a perfect, tight face mask as it touched the skin.

Sssuri went to the pile of cylinders. Choosing one he tinkered with its pointed cone, to be rewarded with a thin hiss.

"Ahhhh—" again his recognition of the rightness of things. "These still contain air." He tested two more and then brought all three back to where Dalgard stood, the canister strapped into place, the mask ready in his hand. With infinite care the merman fitted two of the cylinders into the canister and then was forced to set the other aside.

"We could not change them while under water anyway," he explained. "So it will do little good to take extra supplies with us."

Trying not to speculate on the amount of air he could carry in the cylinders, Dalgard fastened on the mask, adjusted the air tube, and sucked. Air flowed—he could breathe! Only—for how long?

Sssuri, seeing that his companion was fully provided for, worked at the bar locking the sea hatch. But in the end it took their combined strength to spring that barrier and win through to a small cubby which was the actual sea lock.

Dalgard knew one moment of resistance as the merman closed the hatch behind them. For an instant it seemed that the dubious safety of the dressing chamber and a faint hope of the hunters' giving up their vigil was better than what might lie before them now. But Sssuri pushed shut the hatch, and Dalgard stood quietly, without offering any visible protest.

He tried to draw even breaths—slowly—as the merman activated the lock. When the water curled in from hidden openings, rising from ankle to calf and then to knee, its chill striking through flesh to bone, he kept to the same stolid waiting, though this seemed almost worse than a sudden gush of water sweeping them out in its embrace.

The liquid swirled about Dalgard's waist now, tugging at his belt, his arrow quiver, tapping on the bottom of the canister which held his precious air supply. His bow, shielded from the wet by its casing, was swallowed up inch by inch.

As the water lapped at his chin, the outer door opened with a slow inward push which suggested that the machinery controlling it had grown sluggish with the years. Sssuri, perfectly at home, darted out as soon as the opening was large enough to afford him an exit. And his thought came back to reassure the more clumsy landsman.

"We are in the shallows—land rises ahead. The roots of an island. There is nothing to fear—" The word ended abruptly in what was like a mental gasp of either astonishment or fear.

Knowing all the menaces which might lie in wait, even in the shallows of the sea, Dalgard drew his knife once more as he plowed through water—ready to rescue or at least to offer what aid he could.