at the laboratory and the last tanks cleaned. More than ever, the weary Don appreciated the effort that the roboes had gone to make his life easier.

There was now time to study the flood of notes and history from the caves, deciphering those that looked as if they might prove of immediate interest. Even Stone forgot the pain occasioned by his destruction of the protoplasm tanks and became excited over the elusive clue they were following.

"If we could just find the formula the writer hints of," he said to Don at the conclusion of one long session of deciphering. "It's apparent that his ancient civilization had an even more violent revolution by their robots than we have."

"Perhaps if we discover their solution in time, Primo will surrender rather than face a needless annihilation."

Stone shook his head slowly. "No, Don, somehow I don't believe we can escape the problem that easily. Our present civilization and robots must arrive at their own solution. In fact, I'm beginning to wonder why all of this material—" he waved at the mass of papers before them—"has been written by one historian and in such a peculiar style—much as one would write a last will and testament. It surely doesn't sound like a victorious race with an overwhelming force at its command."

A slowly throbbing headache made Don stand up forcibly. "I can't concentrate any more, Doctor. It's maddening to suspect there could be a solution right at our fingertips and yet just a trifle too late to be of any good."

The older man smiled sympathetically. "Why don't you go outside and get some fresh air?" he suggested. "I want to check back and see if perhaps the answer doesn't lie hidden in code, in the material we already have."

Don accepted gratefully and wandered out into the green and restful gardens. The grass was becoming long, he noted; one more task left by the roboes for their masters. He threw himself down beside a fountain and closed his eyes. "Don?" came a whisper.

The soft voice made him start and sit up. Shiela laughed briefly at his nervousness. "Did you think it Primo?"

"I doubt if he'd warn me now."

"But why not, Don? After all, none of the decisions that have been reached were due to you."

"Perhaps not—but I doubt now that any of the roboes could find it 

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