Mandel listened to the Cerian astronomer, wearing a look of sharp disapproval. He said, "Very glib, Dr. Ryger, but quite wrong. I am not as easily fooled by fraudulent demonstrations as you may believe. Now according to the registration data, which I have been forced to check rather hastily, you three were his classmates at college. Is that right?"

They nodded.

"Are there any other classmates of yours present at the Convention?"

"No," said Kaunas. "We were the only four qualifying for a doctorate in astronomy that year. At least he would have qualified except-"

"Yes, I understand," said Mandel. "Well, then, in that case one of you three visited Villiers in his room one last time at midnight."

There was a short silence. Then Ryger said coldly, "Not I." Kaunas, eyes wide, shook his head.

Talliaferro said, "What are you implying?"

"One of you came to him at midnight and insisted on seeing his paper. I don't know the motive. Conceivably, it was with the deliberate intention of forcing him into heart failure. When Villiers collapsed, the criminal, if I may call him so, was ready. He snatched the paper which, I might add, probably was kept under his pillow, and scanned it. Then he destroyed the paper itself in the flash-disposal, but he was in a hurry and destruction wasn't complete."

Ryger interrupted. "How do you know all this? Were you a witness?"

"Almost," said Mandel. "Villiers was not quite dead at the moment of his first collapse. When the criminal left, he managed to reach the phone and call my room. He choked out a few phrases, enough to outline what had occurred. Unfortunately I was not in my room; a late conference kept me away. However, my recording attachment taped it. I always play the recording tape back whenever I return to my room or office. Bureaucratic habit. I called back. He was dead."

"Well, then," said Ryger, "who did he say did it?"

"He didn't. Or if he did, it was unintelligible. But one word rang out clearly. It was 'classmate.' "

Talliaferro detached his scanner from its place in his inner jacket pocket and held it out toward Mandel. Quietly he said, "If you would like to develop the film in my scanner, you are welcome to do so. You will not find Villiers' paper there."

At once, Kaunas did the same, and Ryger, with a scowl, joined.

Mandel took all three scanners and said dryly, "Presumably, whichever one of you has done this has already disposed of the piece of exposed film with the paper on it. However-"

Talliaferro raised his eyebrows. "You may search my person or my room."

But Ryger was still scowling, "Now wait a minute, wait one bloody minute. Are you the police?"

Mandel stared at him. "Do you want the police? Do you want a scandal and a murder charge? Do you want the Convention disrupted and the System press to make a holiday out of astronomy and astronomers? Villiers' death might well have been accidental. He did have a bad heart. Whichever one of you was there may well have acted on impulse. It may not have been a premeditated crime. If whoever it is will return the negative, we can avoid a great deal of trouble."

"Even for the criminal?" asked Talliaferro.

Mandel shrugged. "There may be trouble for him. I will not promise immunity. But whatever the trouble, it won't be public disgrace and life imprisonment, as it might be if the police are called in."

Silence.

Mandel said, "It is one of you three."

Silence.

Mandel went on, "I think I can see the original reasoning of the guilty person. The paper would be destroyed. Only we four knew of the mass-transference and only I had ever seen a demonstration. Moreover you had only his word, a madman's word perhaps, that I had seen it. With Villiers dead of heart failure and the paper gone, it would be easy to believe Dr. Ryger's theory that there was no mass-transference and never had been. A year or two might pass and our criminal, in possession of the mass-transference data, could reveal it little by little, rig experiments, publish careful papers, and end as the apparent discoverer with all that would imply in terms of money and renown. Even his own classmates would suspect nothing. At most they would believe that the long-past affair with Villiers had inspired him to begin investigations in the field. No more."

Mandel looked sharply from one face to another. "But none of that will work now. Any of the three of you who comes through with mass-transference is proclaiming himself the criminal. I've seen the demonstration; I know it is legitimate; I know that one of you possesses a record of the paper. The information is therefore useless to you. Give it up then."

Silence.

Mandel walked to the door and turned again, "I'd appreciate it if you would stay here till I return. I won't be long. I hope the guilty one will use the interval to consider. If he's afraid a confession will lose him his job, let him remember that a session with the police may lose him his liberty and cost him the Psychic Probe." He hefted the three scanners, looked grim and somewhat in need of sleep. "I'll develop these."

Kaunas tried to smile. "What if we make a break for it while you're gone?"

"Only one of you has reason to try," said Mandel. "I think I can rely on the two innocent ones to control the third, if only out of self-protection."

He left

It was five in the morning. Ryger looked at his watch indignantly. "A hell of a thing. I want to sleep."

"We can curl up here," said Talliaferro philosophically. "Is anyone planning a confession?"

Kaunas looked away and Ryger's lip lifted.

"I didn't think so." Talliaferro closed his eyes, leaned his large head back against the chair and said in a tired voice, "Back on the Moon, they're in the slack season. We've got a two-week night and then it's busy, busy. Then there's two weeks of sun and there's nothing but calculations, correlations and bull-sessions. That's the hard time. I hate it. If there were more women, if I could arrange something permanent-"

In a whisper, Kaunas talked about the fact that it was still impossible to get the entire Sun above the horizon and in view of the telescope on Mercury. But with another two miles of track soon to be laid down for the Observatory-move the whole thing, you know, tremendous forces involved, solar energy used directly-it might be managed. It would be managed.

Even Ryger consented to talk of Ceres after listening to the low murmur of the other voices. There was the problem there of the two-hour rotation period, which meant the stars whipped across the sky at an angular velocity twelve times that in Earth's sky. A net of three light scopes, three radio scopes, three of everything, caught the fields of study from one another as they whirled past.

"Could you use one of the poles?" asked Kaunas.

"You're thinking of Mercury and the Sun," said Ryger impatiently. "Even at the poles, the sky would still twist, and half of it would be forever bidden. Now if Ceres showed only one face to the Sun, the way Mercury does, we could have a permanent night sky with the stars rotating slowly once in three years."

The sky lightened and it dawned slowly.

Talliaferro was half asleep, but he kept hold of half-consciousness firmly. He would not fall asleep and leave the others awake. Each of the three, he thought, was wondering, "Who? Who?"-except the guilty one, of course.

Talliaferro's eyes snapped open as Mandel entered again. The sky, as seen from the window, had grown blue. Talliaferro was glad the window was closed. The hotel was air-conditioned, of course, but windows could be opened during the mild season of the year by those Earth-men who fancied the illusion of fresh air. Talliaferro, with Moon-vacuum on his mind, shuddered at the thought with real discomfort.

Mandel said, "Have any of you anything to say?"

They looked at him steadily. Ryger shook his head.

Mandel said, "I have developed the film in your scanners, gentlemen, and viewed the results." He tossed scanners and developed slivers of film on to the bed. "Nothing! you'll have trouble sorting out the film, I'm afraid. For that I'm sorry. And now there is still the question of the missing film."

"If any," said Ryger, and yawned prodigiously.

Mandel said, "I would suggest we come down to Villiers' room, gentlemen."

Kaunas looked startled. "Why?"

Talliaferro said, "Is this psychology? Bring the criminal to the scene of the crime and remorse will wring a confession from him?"

Mandel said, "A less melodramatic reason is that I would like to have the two of you who are innocent help me find the missing film of Villiers' paper."

"Do you think it's there?" asked Ryger challengingly.

"Possibly. It's a beginning. We can then search each of your rooms. The symposium on Astronautics doesn't start till tomorrow at 10 A.M. We have till then."

"And after that?"

"It may have to be the police."

They stepped gingerly into Villiers' room. Ryger was red, Kaunas pale. Talliaferro tried to remain calm.

Last night they had seen it under artificial lighting with a scowling, disheveled Villiers clutching his pillow, staring them down, ordering them away. Now there was the scentless odor of death about it.

Mandel fiddled with the window-polarizer to let more light in, and adjusted it too far, so that the eastern Sun slipped in.

Kaunas threw his arm up to shade his eyes and screamed, "The Sun!" so that all the others froze.

Kaunas's face showed a kind of terror, as though it were his Mercurian sun that he had caught a blinding glimpse of.

Talliaferro thought of his own reaction to the possibility of open air and his teeth gritted. They were all bent crooked by their ten years away from Earth.

Kaunas ran to the window, fumbling for the polarizer, and then the breath came out of him in a huge gasp.

Mandel stepped to his side. "What's wrong?" and the other two joined them.

The city lay stretched below them and outward to the horizon in broken stone and brick, bathed in the rising sun, with the shadowed portions toward them. Talliaferro cast it all a furtive and uneasy glance.

Kaunas, his chest seemingly contracted past the point where he could cry out, stared at something much closer. There, on the outer window sill, one corner secured in a trifling imperfection, a crack in the cement, was an inch-long strip of milky-gray film, and on it were the early rays of the rising sun.