Far Haven — Paul Martin

For his underground humanitarian activities in the shattered world of the future, Zachary Walden is tortured and banished to plague-ridden fourteenth-century England. His fate is made more painful by the knowledge that his own father had invented the time-travel device that America's dictatorial leader uses to rid himself of his enemies. While dealing with the many terrors of the grim past, Zach falls in love with a beautiful but independent farm girl named Tess. After friends from the future finally manage to locate him in his distant exile, Zach must make the difficult choice between revenge and love. Should he return to his old life of struggle or remain in the haven in time he's discovered with Tess?