The child who would have grown up to be Cyrus the Great was killed as an infant. Later, a Time Patrolman, Keith Denison, was forced to play the role of the adult Cyrus returned from hiding to claim his throne. After sixteen years in this role and thirteen years before he is due to fall in battle, Denison is found by a colleague, Everard, and they discuss how to get him out of there. They are in a scenario where history can be changed, hence the need for a Patrol.
If they simply proceed to the twentieth century, then they will arrive in a timeline where Cyrus, who is necessary for post-Exilic Judaism and thus also for Christianity, instead of dying in battle in the twenty ninth year of his reign, disappeared in the sixteenth or seventeenth year of his reign. That is acceptable neither to them nor to the Patrol.
"Suppose I had not showed up? Mightn't Harpagus have found a different psuedo-Cyrus? The exact identity of the King doesn't matter. Another Cyrus would have acted differently from me in a million day-to-day details...But...if he was...reasonably able and decent...then his career would have been the same as mine in all the important ways, the ways that got into the history books." (1)
Here again is the idea of a historical role that could have been played by a different actor. Everard replies that it was Denison's mysterious appearance that gave Harpagus the idea of passing him off as a returned Cyrus.
The eventual solution is for the Patrolmen to prevent the murder of the infant Cyrus who then grows up to play his historical role. To check that history is still on track, they attend a winter solstice festival where they see Cyrus ride past with his courtiers, including Harpagus.
"He's younger than I was...And a little smaller...different face entirely, isn't it?...but he'll do." (2)
Like seeing a remake of the film with a different actor but these guys are doing it with real history! He'll do? He's the right one!
Now something very strange happens to a legendary story. When Everard had arrived in 542 BC, Croesus had told him that Harpagus, ordered to kill the infant Cyrus, instead:
"...exchanged the prince for the stillborn child of a herdsman..." (3)
"...our lord Cyrus grew up as a herdsman." (3)
This story, the one told by Herodotus, is "...a typical hero myth...", told of Moses, Romulus, Sigurd etc, yet is sworn to by eyewitnesses. (4) Everard senses a mystery. Of course, he learns that the infant Cyrus was indeed killed and that the story of his growing up as a herdsman was devised in order to pass off the imposter, Denison, as the returned prince.
Later, he suggests to Denison:
"...all the scientific historians in the future are convinced that the story of Cyrus' childhood as told by Herodotus and the Persians is pure fable. Well, maybe they were right all along. Maybe you experiences here have been only one of those little quirks in space-time which the Patrol tries to eliminate." (5)
So a story that was a lie in the deleted timeline becomes a legend in the revised timeline. The scientific historians do not know what underlies the events that they study.
(1) Anderson, Poul, The Guardians Of Time, New York, 1981, p. 102.
(2) ibid., p. 123.
(3) ibid., p. 83.
(4) ibid., p. 84.