"But you see, we of the other worlds had not lived with these parasites for millions of years, as man and his ancestors had. We had not adapted ourselves to it. Our weak strains had not been killed off gradually through hundreds of generations until only the resistants were left. So, where Earthmen could survive the infection for decades with little harm, we others die a quick death within a year."

"And is that why the incidence has increased since interstellar travel between Earth and the other planets has begun?"

"Yes." For a moment there was silence, and then the Hawkinsite said with a sudden access of energy, "Give me back my cylinder. You have your answer."

Drake said, coolly, "What about the Missing Persons Bureau?" He was swinging the cylinder again; but now the Hawkinsite did not follow its movements. The gray translucent film on his eyes had deepened and Rose wondered whether that was simply an expression of weariness or an example of the changes induced by cyanide lack.

The Hawkinsite said, "As we are not well adapted to the intelligence that infests man, neither is it well adapted to us. It can live on us – it even prefers to, apparently – but it cannot reproduce with ourselves alone as the source of its life. The Inhibition Death is therefore not directly contagious among our people."

Rose looked at him with growing horror. "What are you implying, Dr. Tholan?"

"The Earthman remains the prime host for the parasite. An Earthman may infect one of us if he remains among us. But the parasite, once it is located in an intelligence of the outer worlds, must somehow return to an Earthman, if it expects to reproduce. Before interstellar travel, this was possible only by a re-passage of space and therefore the incidence of infection remained infinitesimal. Now we are infected and reinfected as the parasites return to Earth and come back to us via the mind of Earthmen who travel through space."

Rose said faintly, "And the missing persons – "

"Are the intermediate hosts. The exact process by which it is done, I, of course, do not know. The masculine terrestrial mind seems better suited for their purposes. You’ll remember that at the Institute I was told that the life expectancy of the average human male is three years less than that of the average female. Once reproduction has been taken care of, the infested male leaves, by spaceship, for the outer worlds. He disappears."

"But this is impossible," insisted Rose. "What you say implies that the parasite mind can control the actions of its host! This cannot be, or we of Earth would have noticed their presence."

"The control, Mrs. Smollett, may be very subtle, and may, moreover, be exerted only during the period of active reproduction. I simply point to your Missing Persons Bureau. Why do the young men disappear? You have economic and psychological explanations, but they are not sufficient. – But I am quite ill now and cannot speak much longer. I have only this to say. In the mental parasite, your people and mine have a common enemy. Earthmen, too, need not die involuntarily, except for its presence. I thought that if I found myself unable to return to my own world with my information because of the unorthodox methods I used to obtain it, I might bring it to the authorities on Earth, and ask their help in stamping out this menace. Imagine my pleasure when I found that the husband of one of the biologists at the Institute was a member of one of Earth’s most important investigating bodies. Naturally, I did what I could to be made a guest at his home in order that I might deal with him privately; convince him of the terrible truth; utilize his position to help in the attack on the parasites.

"This is, of course, now impossible. I cannot blame you too far. As Earthmen, you cannot be expected to understand the psychology of my people. Nevertheless, you must understand this. I can have no further dealing with either of you. I could not even bear to remain any longer on Earth."

Drake said, "Then you alone, of all your people, have any knowledge of this theory of yours."

"I atone."

Drake held out the cylinder. "Your cyanide, Dr. Tholan."

The Hawkinsite groped for it eagerly. His supple fingers manipulated the hose and the needle valve with the utmost delicacy. In the space of ten seconds, he had it in place and was inhaling the gas in huge breaths. His eyes were growing clear and transparent.

Drake waited until the Hawkinsite breathings had subsided to normal, and then, without expression, he raised his needle-gun and fired. Rose screamed. The Hawkinsite remained standing. His four lower limbs were incapable of buckling, but his head lolled and from his suddenly flaccid mouth, the cyanide hose fell, disregarded. Once again, Drake closed the needle valve and now he tossed the cylinder aside and stood there somberly, looking at the dead creature. There was no external mark to show that he had been killed. The needle-gun’s pellet, thinner than the needle which gave the gun its name, entered the body noiselessly and easily, and exploded with devastating effect only within the abdominal cavity.

Rose ran from the room, still screaming. Drake pursued her, seized her arm. She heard the hard, flat sounds of his palm against her face without feeling them and subsided into little bubbling sobs.

Drake said, "I told you to have nothing to do with this. Now what do you think you’ll do?"

She said, "Let me go. I want to leave. I want to go away."

"Because of something it was my job to do? You heard what the creature was saying. Do you suppose I could allow him to return to his world and spread those lies? They would believe him. And what do you think would happen then? Can you imagine what an interstellar war might be like? They would imagine they would have to kill us all to stop the disease."

With an effort that seemed to turn her inside out, Rose steadied. She looked firmly into Drake’s eyes and said, "What Dr. Tholan said were no lies and no mistakes, Drake,"

"Oh, come now, you’re hysterical. You need sleep."

"I know what he said is so because the Security Commission knows all about that same theory, and knows it to be true."

"Why do you say such a preposterous thing?"

"Because you yourself let that slip twice."

Drake said, "Sit down." She did so, and he stood there, looking curiously at her. "So I have given myself away twice, have I? You’ve had a busy day of detection, my dear. You have facets you keep well hidden." He sat down and crossed his legs.

Rose thought, yes, she had had a busy day. She could see the electric clock on the kitchen wall from where she sat; it was more than two hours past midnight. Harg Tholan had entered their house thirty-five hours before and now he lay murdered in the spare bedroom.

Drake said, "Well, aren’t you going to tell me where I pulled my two boners?"

"You turned white when Harg Tholan referred to me as a charming hostess. Hostess has a double meaning, you know, Drake. A host is one who harbors a parasite."

"Number one," said Drake. "What’s number two?"

"That’s something you did before Harg Tholan entered the house. I’ve been trying to remember it for hours. Do you remember, Drake? You spoke about how unpleasant it was for Hawkinsites to associate with Earthmen, and I said Harg Tholan was a doctor and had to. I asked you if you thought that human doctors particularly enjoyed going to the tropics, or letting infected mosquitoes bite them. Do you remember how upset you became?"

Drake laughed. "I had no idea I was so transparent. Mosquitoes are hosts for the malaria and yellow fever parasites." He sighed. "I’ve done my best to keep you out of this. I tried to keep the Hawkinsite away. I tried threatening you. Now there’s nothing left but to tell you the truth. I must, because only the truth – or death – will keep you quiet. And I don’t want to kill you."