WHEN HE OPENED HIS eyes there was no sound in the house.

He lay there a moment looking confusedly at the floor. Then, with a startled grunt, he sat up. A package of needles exploded in his head and he slumped down on the cold floor, hands pressed to his throbbing skull. A clicking sound filled his throat as he lay there.

After a few minutes he pulled himself up slowly by gripping the edge of the bench. The floor undulated beneath him as he held on tightly, eyes closed, legs wavering.

A minute later he managed to stumble into the bathroom. There he threw cold water in his face and sat on the bathtub edge pressing a cold, wet cloth to his forehead.

What had happened? He kept blinking and staring at the white-tiled floor.

He stood up and walked slowly into the living room. It was empty. The front door stood half open in the gray of early morning. She was gone.

Then he remembered. He struggled back to the bedroom, using the walls to guide him.

The note was on the bench next to the overturned microscope. He picked up the paper with numbed fingers and carried it to the bed. Sinking down with a groan, he held the letter before his eyes. But the letters blurred and ran. He shook his head and pressed his eyes shut. After a little while he read:

Robert:

Now you know. Know that I was spying on you, know that almost everything I told you was a lie.

I'm writing this note, though, because I want to save you if I can.

When I was first given the job of spying on you, I had no feelings about your life. Because I did have a husband, Robert. You killed him.

But now it's different. I know now that you were just as much forced into your situation as we were forced into ours. We are infected. But you already know that. What you don't understand yet is that we're going to stay alive. We've found a way to do that and we're going to set up society again slowly but surely. We're going to do away with all those wretched creatures whom death has cheated. And, even though I pray otherwise, we may decide to kill you and those like you.

Those like me? he thought with a start. But he kept reading.

I'll try to save you. I'll tell them you're too well armed for us to attack now. Use the time I'm giving you, Robert! Get away from your house, go into the mountains and save yourself. There are only a handful of us now. But sooner or later we'll be too well organized, and nothing I say will stop the rest from destroying you. For God's sake, Robert, go now, while you can!

I know you may not believe this. You may not believe that we can live in the sun for short periods now. You may not believe that my tan was only make-up. You may not believe that we can live with the germ now.

That's why I'm leaving one of my pills.

I took them all the time I was here. I kept them in a belt around my waist. You'll discover that they're a combination of defebrinated blood and a drug. I don't know myself just what it is. The blood feeds the germs, the drug prevents its multiplication. It was the discovery of this pill that saved us from dying, that is helping to set up society again slowly.

Believe me, it's true. And escape!

Forgive me, too. I didn't mean to hit you, it nearly killed me to do it. But I was so terribly frightened of what you'd do when you found out.

Forgive me for having to lie to you about so many things. But please believe this: When we were together in the darkness, close to each other, I wasn't spying on you. I was loving you.

Ruth

He read the letter again. Then his hands fell forward and he sat there staring with empty eyes at the floor. He couldn't believe it. He shook his head slowly and tried to understand, but adjustment eluded him.

He walked unsteadily to the bench. He picked up the small amber pill and held it in his palm, smelled it, tasted it. He felt as if all the security of mason were ebbing away from him. The framework of his life was collapsing and it frightened him.

Yet how did he refute the evidence? The pill, the tan coming off her leg, her walking in the sun, her reaction to garlic.

He sank down on the stool and looked at the mallet lying on the floor. Slowly, ploddingly, his mind went over the evidence.

When he'd first seen her she'd run from him. Had it been a ruse? No, she'd been genuinely frightened. She must have been startled by his cry, then, even though she'd been expecting it, and forgotten all about her job. Then later, when she'd calmed down, she'd talked him into thinking that her reaction to garlic was the reaction of a sick stomach. And she had lied and smiled and feigned hopeless acceptance and carefully got all the information she'd been sent after. And, when she'd wanted to leave, she couldn't because of Cortman and the others. He had awakened then. They had embraced, they had--

His white-knuckled fist jolted down on the bench. "I was loving you." Lie. Lie! His fingers crumpled up the letter and flung it away bitterly.

Rage made the pain in his head flare hotly and he pressed both hands against it and closed his eyes with a groan.

Then he looked up. Slowly he slid off the stool and placed the microscope back on its base.

The rest of her letter wasn't a lie, he knew that. Without the pill, without any evidence of word or memory, he knew. He knew what even Ruth and her people didn't seem to know.

He looked into the eyepiece for a long time. Yes, he knew. And the admission of what he saw changed his entire world. How stupid and ineffective he felt for never having foreseen it! Especially after reading the phrase a hundred, a thousand times. But then he'd never really appreciated it. Such a short phrase it was, but meaning so much.

Bacteria can mutate.