There was an uneasy stir.

Urth said at once, “No need to be afraid of the Probe. Proper handling is safe, particularly if a man offers himself voluntarily. When damage is done, it is usually because of unnecessary resistance, a kind of mental tearing, you know. So if the guilty man will voluntarily confess, place himself in my hands—”

Talliaferro laughed. The sudden noise rang out sharply in the dim quiet of the room. The psychology was so transparent and artless.

Wendell Urth looked almost bewildered at the reaction and stared earnestly at Talliaferro over his glasses. He said, “I have enough influence with the police to keep the Probing entirely confidential.”

Ryger said savagely, “I didn’t do it.”

Kaunas shook his head.

Talliaferro disdained any answer.

Urth sighed. “Then I will have to point out the guilty man. It will be traumatic. It will make things harder.” He tightened the grip on his belly and his fingers twitched. “Dr. Talliaferro pointed out that the film was hidden on the outer window sill so that it might remain safe from discovery and from harm. I agree with him.”

“Thank you,” said Talliaferro dryly.

“However, why should anyone think that an outer window sill is a particularly safe hiding place? The police would certainly look there. Even in the absence of the police it was discovered. Who would tend to consider anything outside a building as particularly safe? Obviously, some person who has lived a long time on an airless world and has it drilled into him that no one goes outside an enclosed place without detailed precautions.

’To someone on the Moon, for instance, anything hidden outside a Lunar Dome would be comparatively safe. Men venture out only rarely and then only on specific business. So he would overcome the hardship of opening a window and exposing himself to what he would subconsciously consider a vacuum for the sake of a safe hiding place. The reflex thought, ‘Outside an inhabited structure is safe,’ would do the trick.”

Talliaferro said between clenched teeth, “Why do you mention the Moon, Dr. Urth?”

Urth said blandly, “Only as an example. What I’ve said so far applies to all three of you. But now comes the crucial point, the matter of the dying night.”

Talliaferro frowned. “You mean the night Villiers died?”

“I mean any night. See here, even granted that an outer window sill was a safe hiding place, which of you would be mad enough to consider it a safe hiding place for a piece of unexposed film? Scanner film isn’t very sensitive, to be sure, and is made to be developed under all sorts of hit-and-miss conditions. Diffuse night-time illumination wouldn’t seriously affect it, but diffuse daylight would ruin it in a few minutes, and direct sunlight would ruin it at once. Everyone knows that.”

Mandel said, “Go ahead, Urth. What is this leading to?”

“You’re trying to rush me,” said Urth, with a massive pout. “I want you to see this clearly. The criminal wanted, above all, to keep the film safe. It was his only record of something of supreme value to himself and to the world. Why would he put it where it would inevitably be ruined by the morning sun?—Only because he did not expect the morning sun ever to come. He thought the night, so to speak, was immortal.

“But nights aren’t immortal. On Earth, they die and give way to daytime. Even the six-month polar night is a dying night eventually. The nights on Ceres last only two hours; the nights on the Moon last two weeks. They are dying nights, too, and Dr. Talliaferro and Ryger know that day must always come.”

Kaunas was on his feet. “But wait—”

Wendell Urth faced him full. “No longer any need to wait, Dr. Kaunas. Mercury is the only sizable object in the Solar System that turns only one face to the sun. Even taking libration into account, fully three-eighths of its surface is true dark-side and never sees the sun. The Polar Observatory is at the rim of that dark-side. For ten years, you have grown used to the fact that nights are immortal, that a surface in darkness remains eternally in darkness, and so you entrusted unexposed film to Earth’s night, forgetting in your excitement that nights must die—”

Kaunas stumbled forward. “Wait—”

Urth was inexorable. “I am told that when Mandel adjusted the polarizer in Villiers’ room, you screamed at the sunlight. Was that your ingrained fear of Mercurian sun, or your sudden realization of what sunlight meant to your plans? You rushed forward. Was that to adjust the polarizer or to stare at the ruined film?”

Kaunas fell to his knees. “I didn’t mean it. I wanted to speak to him, only to speak to him, and he screamed and collapsed. I thought he was dead and the paper was under his pillow and it all just followed. One thing led on to another and before I knew it, I couldn’t get out of it anymore. But I meant none of it. I swear it.”

They had formed a semicircle about him and Wendell Urth stared at the moaning Kaunas with pity in his eyes.

An ambulance had come and gone. Talliaferro finally brought himself to say stiffly to Mandel, “I hope, sir, there will be no hard feelings for anything said here.”

And Mandel had answered, as stiffly, “I think we had all better forget as much as possible of what has happened during the last twenty-four hours.”

They were standing in the doorway, ready to leave, and Wendell Urth ducked his smiling head, and said, “There’s the question of my fee, you know.”

Mandel looked startled.

“Not money,” said Urth at once. “But when the first mass-transference setup for humans is established, I want a trip arranged for me.”

Mandel continued to look anxious. “Now, wait. Trips through outer space are a long way off.”

Urth shook his head rapidly. “Not outer space. Not at all. I would like to step across to Lower Falls, New Hampshire.”

“All right. But why?”

Urth looked up. To Talliaferro’s outright surprise, the extra-terrologist’s face wore an expression compounded of shyness and eagerness.

Urth said, “I once—quite a long time ago—knew a girl there. It’s been many years—but I sometimes wonder—”