Cryptozoic! — Brian W. Aldiss

He roamed through the dim reaches of the remote past and like a phantom, the Dark Woman haunted him at every turn. Was she a hallucination produced by the stresses of his bizarre existence? Or was she a ghost from a future more distant than his own?

Bush had been called into a totalitarian world, trained to kill, and then sent back in time â€" as an assassin. And still the Dark Woman pursued him, posing new questions, new possibilities, new terrors…