A Bridge Of Years - Robert Charles Wilson

Tom Winter thought the secluded cottage in the Pacific Northwest would be the perfect refuge—a place to nurse the wounds of lost love and happiness. But Tom soon discovers that his safe haven is the portal of a tunnel through time. At one end is the present. At the other end—New York City, 1963.

His journey back to the early 1960s seems to offer him the chance to start over in a simpler, safer world. But he finds that the tunnel holds a danger far greater than anything he left behind: a human killing machine escaped from a bleak and brutal future, who will do anything to protect the secret passage that he thought was his alone. To preserve his worlds, past and present, Tom Winter must face the terrors of an unknown world to come.
From Robert Charles Wilson, the Hugo Award-winning author of Spin, A Bridge of Years is a classic science fiction story of time-travel and human transformation.