"Eric, it couldn't be." He paced up and down the floor, clasping and unclasping his hands. "I don't know. It came without warning on a night when nearly everyone was out celebrating. No one in the streets or parks could have been prepared for it. Most of the dwellings were probably left with windows opened. It's only sheer luck that it wasn't the case here. And luck again that we came back early." "Please sit down," she begged. He looked at her a moment, then shrugged, came over to the sofa, and sat beside her. "There must have been some, Eric," she said. "The law of averages would seem to indicate that. There might be some who are naturally immune to whatever brand of poison this is; some who escaped as did we; some who were underground, or in forests. But until we learn differently, we must assume that we are the only humans alive." His eyes were haunted. "How could we have missed it?" he whispered. "We checked and re-checked all the data, and put it to the calculating machines. The answer was the same each time: no such cloud existed." "Perhaps there were some factors that only Greer himself knew. Some small items concerning his calculations which he overlooked in presenting data, not realizing that it had influenced him. If one factor were missing, known only to Greer, then all the machines in the world might well give a negative result." He shook his head. "It's fantastic--yet, what can we think? If your idea of a missing factor is correct, we'll never know. Even if Greer is still alive. He was cured of his delusion." She was silent for a moment, then she slipped off her gloves, laid a hand on his arm. "Eric," she whispered. "I'm sorry it had to happen at a time like this. It may be that Sandra escaped, too. I know what she means to you. If we find her, later, I shan't stand in the way." He chewed his lips. "That's all over, now. The first thing we must do is to check up on the food, water, and sanitation system. Just how long the machines will run without human supervision is questionable--not long, at any rate. The robots cannot do everything alone, either." Her eyes were calm and clear, her voice a breath of cool air in the heat of his anguish. "Then let's do it the same way, Eric. Nothing is going to happen for awhile. Let's tackle the problem after we're refreshed." She moved to free herself from him; he had, automatically, slipped his arm around her waist, drawn her to him. "You--you can use the lab for your quarters. Good night, Eric." He held her back. "Natalla." "Let me go," she murmured. "Natalla, wait. I didn't tell you all I saw. It was more than--the cloud." He fell silent, breathing rapidly. "Well?" she said. "I was reading some of the old books yesterday. Some of them centuries old. The people then, most of them, didn't live as well as we do but they were very much like us in some other ways.