The Meddler by Philip K. Dick - The hardest part of the "preordained" thesis to grasp is that the thesis itself is part of what must and shall be. Will time travel cause the end of the human race? Or will it allow them to fix the future?

They entered the great chamber. At the far end, technicians hovered around an immense illuminated board, following a complex pattern of lights that shifted rapidly, flashing through seemingly endless combinations. At long tables machines whirred — computers, human-operated and robot. Wall-charts covered every inch of vertical space. Hasten gazed around him in amazement.

Wood laughed. "Come over here and I'll really show you something. You recognize this, don't you?" He pointed to a hulking machine surrounded by silent men and women in white lab robes.

"I recognize it," Hasten said slowly. "It's something like our own Dip, but perhaps twenty times larger. What do you haul up? And when do you haul?" He fingered the surface-plate of the Dip, then squatted down, peering into the maw. The maw was locked shut; the Dip was in operation. "You know, if we had any idea this existed, Histo-Research would have —"

"You know now." Wood bent down beside him. "Listen. Hasten, you're the first man from outside the Department ever to get into this room. You saw the guards. No one gets in here unauthorized; the guards have orders to kill anyone trying to enter illegally."

"To hide this? A machine? You'd shoot to —"

They stood, Wood facing him, his jaw hard. "Your Dip digs back into antiquity. Rome. Greece. Dust and old volumes." Wood touched the big Dip beside them. "This Dip is different. We guard it with our lives, and anyone else's lives; do you know why?"

"This Dip is set, not for antiquity, but — for the future." Wood looked directly into Hasten's face. "Do you understand? The future." "You're dredging the future? But you can't! It's forbidden by law; you know that!"