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............