tared into Mark's eyes.

"How much do you know about time?" he demanded.

* * * * *

"Time?"

"Yes. And time travel."

The younger man shrugged.

"Practically nothing," he admitted. "Oh, I've read a few stories, of
course. But that's all. I don't know what the theory of it all is, if
that's what you mean."

"I thought so." Professor Duchard sighed. "That being the case, there is
little use in my wasting energy trying to give you any real
understanding of it.

"However, I can tell you this: time is not the immutable thing most
people presume it to be. Actually, it is only another dimension. As a
research physicist, I have for many years been convinced of this."

"You mean that time travel really is possible? That men can be
transported into the future or the past--"

The other held up a restraining hand.

"Yes. Time travel _is_ possible, if men could break through into that
other dimension." A pause. "Yet up until tonight, I never believed that
man had found a way to pass that barrier."

"But professor! Think what you're saying! You're telling me that I could
go back and murder my own grandfather. That I could prevent myself from
being born--"

Again the elder man sighed.

"I was afraid of this," he said. "I knew you could not understand." He
hesitated. Then: "At any rate, take my word for it that time travel is
possible. Also, I assure you that there are any number of perfectly
sound theoretical and practical reasons why you never could hope to
murder your grandparents."

The other brushed the words aside.

"What about Elaine? What's all this got to do with her?"

"Everything. You see, my boy, it is _not_ possible for us to transport
our material bodies across time. They cannot bridge the gap. They must
remain in the period in which they are born--"

"But Elaine--"

Never had Mark seen the white-haired savant so solemn. His aged face was
drawn with worry. Yet there was terrifying self-confidence in his words.

"Elaine," he said quietly, "at this moment is trapped in time!"

* * * * *

There was a moment of stunned silence, then. Mark's brain was spinning.
He stared at Professor Duchard through narrowed eyes, half-convinced
that the man was mad. And yet--

"I am not insane," the scientist declared, as if answering an unspoken
question. "Believe me, my boy, I am not."

"Go on."

"That mirror which Adrian Vance sent to my daughter