Liminal States

Liminal States is a novel by Zack Parsons, published in March 2012. The story principally follows two men, Warren Groves and Gideon Long, who become immortal in 1874 through a process they don't fully understand. Over the course of three sections, set in 1874, 1951 and 2006, the story follows their lives across an increasingly divergent alternate history America. As part of the build-up to the novel's release, Parsons also published a related serial, "The Reificant," following an alien's encounter with the same form of immortality.