Ad Infinitum — James Wright

High-stakes politics and a stolen thermonuclear warhead are only the beginning for one CIA agent. Robert Gray, sent in on a deadly mission to disarm a terrorist group plotting Armageddon, falls prey to a nuclear deathtrap. But death is not an option.

Instead, Robert finds himself explicably traveling through time, and he soon discovers that he is being pursued by a much more powerful traveler. He must now discover the secret behind his own traveling, and he must learn the hidden motives of his indomitable pursuer. This time, the truth will either kill him
or set him free.