"I still don't understand you, Bigman."

"I think you do, David Starr." He nearly shouted the name in Ms triumph.

David said, "Quiet, man!"

Bigman's voice sank. "I've seen you in video reels often enough. But why don't your wrists show the mark? I've heard all the members of the Council were marked."

"Where did you hear this? And who told you the library at Canal and Phobos is the Council of Science?"

Bigman flushed. "Don't look down at the farmboy, mister. I've lived in the city. I've even had schooling."

"My apologies. I didn't mean it that way. Will you still help me?"

"Not until I understand about your wrists."

"That's not hard. It's a colorless tattoo that will turn dark in air, but only if I want it to."

"How's that?"

"It's a matter of emotion. Each human emotion is accompanied by a particular hormone pattern in the blood. One and only one such pattern activates the tattoo. I happen to know the emotion that fits."

David did nothing visibly, but slowly a patch on the inner surface of his right wrist appeared and darkened. The golden dots of the Big Dipper and Orion glowed momentarily and then the whole faded rapidly.

Bigman's face glowed and his hands came down for that automatic smack against his boots. David caught Ms arms roughly.

"Hey," said Bigman.

"No excitement, please. Are you with me?"

"Sure I'm with you. I'll be back tonight with the stuff you want and I'll tell you where we can meet.

There's a place outside, near the Second Section____________________ "

He went on, whispering directions.

David nodded. "Good. Here's the envelope."

Bigman took it and inserted it between his hip boot and thigh. He said, "There's a pocket on the inside top of the better-quality hip boots, Mr. Starr. Do you know that?"

"I do. Don't look down at this farmboy, either. And my name, Bigman, is still Williams. That leaves just one last statement. The Council librarians will be the only ones who will be able to open that envelope safely. If anyone else tries, he'll be hurt."

Bigman drew himself up. "No one else will open it. There are people who are bigger than I am. Maybe you think I don't know that, but I do. Just the same, bigger or not, nobody, and I mean nobody, will take this from me without killing me. What's more, I wasn't thinking of opening it myself, either, if you've given that any thought."

"I have," said David. "I try to give all possibilities some, thought, but I didn't give that one very much."

Bigman smiled, made a mock pass with his fist at David's chin, and was gone.

It was almost dinnertime when Benson returned. He looked unhappy and his plump cheeks were drooping.

He said listlessly, "How are you, Williams?"

David was washing his hands by dipping them into the special detergent solution which was universally used on Mars for this purpose. He withdrew his hands into the stream of warm air for drying, while the wash water flushed away into the tanks where it could be purified and returned to the central supply. Water was expensive on Mars and was used and reused wherever possible.

David said, "You look tired, Mr. Benson."

Benson closed the door carefully behind him. He blurted it out. "Six people died yesterday of the poisoning. That's the highest number yet for a single day. It's getting worse all the time and there's nothing we seem to be able to do."

He glowered at the lines of animal cages. "All alive, I suppose."

"All alive," said David.

"Well, what can I do? Every day Makian asks me if I have discovered anything. Does he think I can find discoveries under my pillow in the morning? I was in the grain bins today, Williams. It was an ocean of wheat, thousands and thousands of tons all set for shipment to Earth. I dipped into it a hundred times. Fifty grains here; fifty grains there. I tried every corner of every bin. I had them dip twenty feet down for samples. But what good is it? Under present conditions it would be a generous estimate to suppose that one out of a billion grains is infected."

He nudged at the suitcase he had brought with him. "Do you think the fifty thousand grains I've got here have the one in a billion among them? One chance in twenty thousand!"

David said, "Mr. Benson, you told me that no one ever died on the farm here, even though we eat Martian food almost exclusively."

"Not as far as I know."

"How about Mars as a whole?"

Benson frowned. "I don't know. I suppose not or I would have heard of it. Of course life isn't as tightly organized here on Mars as it is on Earth. A farmboy dies and usually he is simply buried without formality. There are few questions." Then, sharply, "Why do you ask?"

"I was just thinking that if it were a Martian germ, people on Mars might be more accustomed to it than Earth people. They might be immune."

"Well! Not a bad thought for a non-scientist. In fact, it's a good idea. I'll keep it in mind," He reached up to pat David's shoulder. "You go on and eat. We'll begin feeding the new samples tomorrow."

As David left, Benson turned to his suitcase and was lifting out the carefully labeled little packets, one of which might hold the all-important poisoned kernel. By tomorrow those samples would be ground, each little pile of powder carefully mixed and painstakingly divided into twenty sub-samples, some for feeding and some for testing.

By tomorrow! David smiled tightly to himself. He wondered where he would be tomorrow. He even wondered if he would be alive tomorrow.

The farm dome lay asleep like a giant prehistoric monster curled upon the surface of Mars. The residual fluorescents were pale glimmers against the dome roof. Amid the silence the ordinarily unheard vibrations of the dome's atmospherics, which compressed Martian atmosphere to the normal Earth level and added moisture and oxygen from the quantities supplied by the growing plants of the vast greenhouses, sounded in a low grumble.

David was moving quickly from shadow to shadow with a caution that was, to a large extent, not necessary. There was no one watching. The hard composition of the dome was low overhead, bending rapidly to the ground, when he reached Lock 17. His hair brushed it.

The inner door was open and he stepped inside. His pencil flashlight swept the walls within and found the controls. They weren't labeled, but Bigman's directions had been clear enough. He depressed the yellow button. There was a faint click, a pause, and then the soughing of air. It was much louder than it had been on the day of the checkup, and since the lock was a small one designed for three or four men rather than a giant one designed for nine sand-cars, the air pressure dropped much more quickly.

He adjusted his nosepiece, waited for the hissing to die away, the silence indicating pressure equilibrium. Only then did he depress the red button. The outer section lifted and he stepped out.

This time he was not trying to control a car. He lowered himself to the hard, cold sands and waited for the stomach-turning sensations to pass as he accustomed himself to the gravity change. It took scarcely two minutes for that to happen. A few more gravity-change passages, David thought grimly, and he would have what the farmboys called "gravity legs."

He rose, turned to get his bearings, and then found himself, quite involuntarily, frozen in fascination!

It was the first time he had ever seen the Martian night sky. The stars themselves were the old familiar ones of Earth, arranged in all the familiar constellations. The distance from Mars to Earth, great though it was, was insufficient to alter perceptibly the relative positions of the distant stars. But though the stars were unchanged in position, how vastly they were changed in brilliance.