"Of course he couldn't," said the Doctor, passing her a crumpet.
With the addition of the brat to the TARDIS crew, the Doctor had gone all hospitality and insisted that the four of them sit down to tea before Tegan showed Turlough the TARDIS and to a room of his own. This had been fine with Tegan, actually. The only unoccupied bedroom she knew of, at least to locate, was Adric's, and she didn't like the idea of anyone else staying there, least of all the brat. Maybe this would kill enough time for her to come up with another option. Well, she hadn't liked Adric much at the beginning either; perhaps she just needed to spend some time with Turlough.
"You can't remember something," the Doctor continued, "that hasn't happened yet."
"But it had happened," Turlough objected, "in 1977." Turlough had accepted the Doctor's suggestion of a tea with polite enthusiasm. Tegan had no idea what he really thought about it.
"If time were so linear as that," said the Doctor, "time travel itself would be impossible." He was blowing on his tea; so far it had been too hot for him.
Nyssa asked, "So you're saying that it hadn't happened in 1977, yet?"
"Exactly!" said the Doctor, beaming at Nyssa the way he did when she'd said something clever.
"But he remembered Tegan in 1983," Turlough rebutted, "before you reactivated the pod."
"He did?" Tegan perked up. "I hadn't heard." Well, if the Brigadier'd taken that much notice of her, maybe she'd forgive him for siding with Nyssa when Mawdyrn'd claimed to be the regenerated Doctor.
Turlough gave her that ingratiating smile of his, but she ignored it for her interest in the story. "While we were investigating the pod, he remembered you, and gradually he remembered the events leading up to the your return in the TARDIS to the spaceliner."
"Ah, but he also remembered incorrectly," the Doctor reminded Turlough, "that he hadn't gone to the spaceliner in the TARDIS in 1977. At that point he was remembering only those parallel events that had already occurred in the 1977 current of the causal event timestream. The false memory that he had stayed behind was probably just a compensation, a rationalization by his conscious mind for that he didn't remember what would happen next - because, as I say, it hadn't happened yet."
"And when the 1983 Brigadier saw the 1977 Brigadier," prompted Nyssa, "and said, 'I remember'?"
"Well, of course he remembered then," said the Doctor, "or at least everything from the 1977 current that had happened so far; which happened to be everything, since he was unconscious in 1977 from then until the TARDIS left him on the school campus again."
"And this is how it would work with anyone who crossed his own timestream?" Turlough asked.
The Doctor had been trying his tea again. For a moment it had seemed he found it all right, but suddenly it seemed still too hot after all. "Well," said the Doctor, ineffectually wiping at the front of his sweater, "obviously no ethical time-traveler brings about such a situation purposefully, or only in cases of extreme emergency; or, rarely, by accident, such as this time. Consequently there isn't any body of scientifically recorded observation. But I have, er, reason to believe that that's the case."
Tegan eyed him warily. He was covering something. "I think you're making all this up," she said. "You have no way of knowing."
"Well," the Doctor said, "time you were showing Turough around the TARDIS."
Rabbits, thought Tegan.
THE END