"My work here is nearly ended," said Karellen's voice from a million radios.

"There are many things we have had to hide from you, as we hid ourselves for half our stay on Earth. Some of you, I know, thought that concealment unnecessary. You are accustomed to our presence: you can no longer imagine how your ancestors would have reacted to us. But at least you can understand the purpose of our concealment, and know that we had a reason for what we did.

"A century ago we came to your world and saved you from self-destruction. I do not believe that anyone would deny that fact -- but what that self-destruction was, you never guessed.

"Because we banned nuclear weapons and all the other deadly toys you were accumulating in your armouries, the danger of physical annihilation was removed. You thought that was the only danger. We wanted you to believe that, but it was never true. The greatest danger that confronted you was of a different character altogether -- and it did not concern your race alone.

"The supreme secret we kept from you was our purpose in coming to Earth -- that purpose about which you have speculated so endlessly. We could not tell you until now, for the secret was not ours to reveal.

"At last, after a hundred years, I can tell you what it was.

"Many worlds have come to the crossroads of nuclear power, have avoided disaster, have gone on to build peaceful and happy civilizations -- and have then been utterly destroyed by forces of which they knew nothing. In the twentieth century, you first began to tamper seriously with those forces. That was why it became necessary to act.

"All through that century, the human race was drawing slowly nearer to the abyss -- never even suspecting its existence. Across that abyss, there is only one bridge. Few races, unaided, have ever found it. Some have turned back while there was still time, avoiding both the danger and the achievement. Their worlds have become Elysian islands of effortless content, playing no further part in the story of the universe. That would never have been your fate -- or your fortune. Your race was too vital for that. It would have plunged into ruin and taken others with it, for you would never have found the bridge.

"I am afraid that almost all I have to say now must be by means of such analogies. You have no words, no conceptions, for many of the things I wish to tell you -- and our own knowledge of them is also sadly imperfect.

"Yet your mystics, though they were lost in their own delusions, had seen part of the truth. There are powers of the mind, and powers beyond the mind, which your science could never have brought within its framework without shattering it entirely. All down the ages there have been countless reports of strange phenomena -- poltergeists, telepathy, precognition -- which you had named but never explained. At first Science ignored them, even denied their existence, despite the testimony of five thousand years. But they exist, and, if it is to be complete, any theory of the universe must account for them.

"In the centuries before our coming, your scientists uncovered the secrets of the physical world and led you from the energy of steam to the energy of the atom. You had put superstition behind you: Science was the only real religion of mankind. It was the gift of the western minority to the remainder of mankind, and it had destroyed all other faiths. Those that still existed when we came were already dying. Science, it was felt, could explain everything: there were no forces which did not come within its scope, no events for which it could not ultimately account. The origin of the universe might be forever unknown, but all that had happened after obeyed the laws of physics.

"To understand, you must go back into the past and recover much that your ancestors would have found familiar, but which you have forgotten -- which, in fact, we deliberately helped you to forget. For all our sojourn here has been based on a vast deception, a concealment of truth which you were not ready to face.

"And so we came -- we were sent -- to Earth. We interrupted your development on every cultural level, but in particular we checked all serious work on paranormal phenomena. I am well aware of the fact that we have also inhibited, by the contrast between our civilizations, all other forms of creative achievement as well. But that was a secondary effect, and it is of no Importance.

"That could not be allowed. I cannot explain the full nature of the threat you represented. It would not have been a threat to us, and therefore we do not comprehend it. Let us say that you might have become a telepathic cancer, a malignant mentality which in its inevitable dissolution would have poisoned other and greater minds.

"During the first half of the twentieth century, a few of your scientists began to investigate these matters. They did not know it, but they were tampering with the lock of Pandora's box. The forces they might have unleashed transcended any perils that the atom could have brought. For the physicists could only have ruined the Earth: the paraphysicists could have spread havoc to the stars.

"Now I must tell you something which you may find very surprising, perhaps almost incredible. All these potentialities, all these latent powers -- we do not possess them, nor do we understand them. Our intellects are far more powerful than yours, but there is something in your minds that has always eluded us. Ever since we came to Earth we have been studying you; we have learned a great deal, and will learn more, yet I doubt if we shall discover all the truth.

"We held the clock back, we made you mark time while those powers developed, until they could come flooding out into the channels that were being prepared for them. What we did to improve your planet, to raise your standards of living, to bring justice and peace -- those things we should have done in any event, once we were forced to intervene in your affairs. But all that vast transformation diverted you from the truth, and therefore helped to serve our purpose.

"Our races have much in common -- that is why we were chosen for this task. But in other respects, we represent the ends of two different evolutions. Our minds have reached the end of their development. So, in their present form, have yours. Yet you can make the jump to the next stage, and therein lies the difference between us. Our potentialities are exhausted, but yours are still untapped. They are linked, in ways we do not understand, with the powers I have mentioned -- the powers that are now awakening on your world.

"We believe -- it is only a theory -- that the Overmind Is trying to grow, to extend its powers and its awareness of the universe. By now it must be the sum of many races, and long ago it left the tyranny of matter behind. It is conscious of intelligence, everywhere. When it knew that you were almost ready, it sent us here to do its bidding, to prepare you for the transformation that is now at hand.

"We are your guardians -- no more. Often you must have wondered what position my race held in the hierarchy of the universe. As we are above you, so there is something above us, using us for its own purposes. We have never discovered what it is, though we have been its tool for ages and dare not disobey it. Again and again we have received our orders, have gone to some world in the early flower of its civilization, and have guided it along the road that we can never follow -- the road that you are travelling now.

"Again and again we have studied the process we have been sent to foster, hoping that we might learn to escape from our own limitations. But we have glimpsed only the vague outlines of the truth. You called us the Overlords, not knowing the irony of that title. Let us say that above us is the Overmind, using us as the potter uses his wheel. And your race is the clay that is being shaped on that wheel.

"As to the nature of that change, we can tell you very little. We do not know how it is produced -- what trigger impulse the Overmind employs when it judges that the time is ripe. All we have discovered is that it starts with a single individual -- always a child -- and then spreads explosively, like the formation of crystals round the first nucleus in a saturated solution. Adults will not be affected, for their minds are already set in an unalterable mould.

"All the earlier changes your race has known took countless ages. But this is a transformation of the mind, not of the body. By the standards of evolution, it will be cataclysmic -- instantaneous. It has already begun. You must face this fact: yours is the last generation of Homo sapiens.

"In a few years, it will all be over, and the human race will have divided in twain. There is no way back, and no future for the world you know. All the hopes and dreams of your race are ended now. You have given birth to your successors, and it is your tragedy that you will never understand them -- will never even be able to communicate with their minds. Indeed, they will not possess minds as you know them. They will be a single entity, as you yourselves are the sums of your myriad cells. You will not think them human, and you will be right.

"For what you have brought into the world may be utterly alien, it may share none of your desires or hopes, it may look upon your greatest achievements as childish toys -- yet it is something wonderful, and you will have created it.

"I have told you these things so that you will know what faces you. In a few hours, the crisis will be upon us. My task and my duty is to protect those I have been sent here to guard. Despite their wakening powers, they could be destroyed by the multitudes around them -- yes, even by their parents, when they realize the truth. I must take them away and isolate them, for their protection, and for yours. Tomorrow my ships will begin the evacuation. I shall not blame you if you try to interfere, but it will be useless. Greater powers than mine are wakening now; I am only one of their instruments.

"When our race is forgotten, part of yours will still exist. Do not, therefore, condemn us for what we were compelled to do. And remember this -- we shall always envy you."

"And then -- what am I to do with you, the survivors, when your purpose has been fulfilled? It would be simplest, perhaps, and most merciful, to destroy you -- as you yourselves would destroy a mortally wounded pet you loved. But this I cannot do. Your future will be your own to choose in the years that are left to you. It is my hope that humanity will go to its rest in peace, knowing that it has not lived in vain.