“There were certain stones of great power mentioned in the old legends. The Lia Fail of the Tuatha De Danann of Ireland. When the rightful king trod upon it, it shouted aloud in his honor. It was the coronation stone of that race, one of their three great treasures. And do not the kings of England to this day still cherish the Stone of Scone beneath their throne?

“But in Cornwall there was another stone of power — the Siege Perilous. It was one rumored to be able to judge a man, determine his worth, and then deliver him to his fate. Arthur was supposed to have discovered its power through the Seer Merlin and incorporated it among the seats of the Round Table. Six of his knights tried it — and disappeared. Then came two who knew its secret and stayed: Percival and Galahad.”

“Look here.” Simon was bitterly disappointed, the more so because he had almost dared to hope again. Petronius was cracked, there was no escape after all.

“Arthur and the Round Table — that’s a fairy tale for kids. You’re talking as if—”

“As if it were true history?” Petronius caught him up. “Ah, but who is to say what is history and what is not? Every word of the past which comes to us is colored and influenced by the learning, the prejudices, even the physical condition of the historian who has recorded it for later generations. Tradition fathers history and what is tradition but word of mouth? How distorted may such accounts become in a single generation? You, yourself, had your entire life changed by perjured testimony. Yet that testimony has been inserted in records, has now become history, untrue as it is. How can anyone say that this story is legend but that one a fact, and know that he is correct? History is made, is recorded by human beings, and it is larded with all the errors our species is subject to. There are scraps of truth in legend and many lies in accepted history. I know — for the Siege Perilous does exist!

“There are also theories of history alien to the conventional ones we learn as children. Have you ever heard of the alternate worlds which may stem from momentous decisions? In one of those worlds, Colonel Tregarth, perhaps you did not turn aside your eyes on that night in Berlin. In another you did not meet with me an hour ago, but went on to keep your rendezvous with Sammy!”

The doctor rocked back and forth on his heels, as if set teetering by the force of his words and belief. And in spite of himself Simon caught a bit of that fiery enthusiasm.

“Which of these theories do you intend to apply to my problem?”