Mark's voice was fierce.
"What's wrong with it? What's to stop me?"
The other sighed. Brushed back white hair with a sweep of one frail hand.
"You cannot change history, my boy," he said sadly. "A study of cosmology would show you that such things are immutable. You can go backward or forward through time and participate in them, but you cannot change them."
"How do you know? Who's traveled through time and then come back to say we can't change events?"
"You do not understand—"
"And I don't care!" the younger man flared. "I may fail—but I'm going to try! I'm not going to sit here, waiting for Elaine to die—"
"But you would have no memory of your life in this century! Remember what Vance said—"
"Right. That's the one thing that might stop me. I'm counting on you to take care of it, though. Is there anything you can do?"
There was a long moment of tension-studded silence. Then: