"Why," Isis asked, as the CAVE began coming in for a landing, "doesn't going back and forth through time make you meet people in the wrong order?"
"Convergence limitation," said Nimue immediately, precisely because she knew she'd never defined the term to Isis.
"Which means?" Was that the expression Merlin had always complained to Nimue for? Nimue had seen it on Pelleas from time to time ...
"I could show you the math," she offered, just so Isis knew Nimue knew Isis knew Nimue was being difficult.
"Thank you, no." Well-bred at least, this one.
"Being recognized by someone I never met is something that almost never happens," Nimue came clean. "There was a chap called Set who knew Merlin. But time-travel is like climbing something," she added quickly, though not quickly enough to sound as if she was avoiding a subject, "say a tree trunk on Dacaenas III, that's a spiral or corkscrew shape. It's easy to drop from this loop to the one below, or perhaps to reach up and pull yourself onto the one above, but it's much more difficult to just crawl back and forth along the loop you're on. Few people have lifespans that encompass more than a fraction of one loop."
"What about institutions?" Isis asked, as Nimue swung the CAVE door lever and led her toward the exit. "Are you known to my civilization in other times, as you are in mine?"
Twice in a minute she'd had to dodge that bullet! But Nimue wasn't going to saddle Isis with this time paradox when there was no need - bad enough she'd let on as much as she'd done to Amun and Geb. "I'm not all that well known in the Dynasty," she said, a half-truth. "In fact I purposely try - and Merlin before me - to remain unnoticed by, to use your word, institutions, the obvious exception having been the Round Table and the starcruiser Excalibur. Not so much to keep from running into people who already know us, but to keep down the chances of an institution that has come to know us in one era discovering us too soon."
Even as she spoke, she and Isis closed the CAVE door behind them, and noted that they'd materialized in the cramped corridor of a spaceship. Simultaneous with their departure from the CAVE, a group of uniformed people entered the corridor from a room partway down the hall.
"Who are you?" demanded the man in the lead, a young man with an open face.
They were startled, not only by the time-travelers' presence, but by Isis' felinoid features; the young queen hailed from the earliest era of humanoid occupation of the universe, when the gods had not yet gotten the laws of genetics quite settled in their minds.
But Nimue was no less startled by them. For she knew them, though their uniforms were oddly unfamiliar - and they were younger than when she had met them.
One was a prince of the planet Benwick, one was a princess of the planet Camelaird ... and the speaker was King Arthur Pendragon of Camelot.