In a society where images of the past can be viewed exactly as they happen, one man tests a radical theory that the past can be entered and changed, bringing two worlds into collision that threaten to destroy the fabric of space and time. In the sequel to Timeshift, Tobias Raikhel succeeds in opening a window in time that brings two civil war soldiers from 1863 five hundred years into the future, with potentially disastrous consequences for both worlds.
Paul Thorndyke, age 45, now controls the time viewing process. His life-long friend Quentin Cottle persuades him to test the radical theory that the past can be entered and changed. Cottle wants to go back in time and destroy the deadly ash that plagues humanity before it has a chance to spread. When Cottle is accidentally lost in the past, all memory of him in the future instantly vanishes. Thorndyke feels a great loss, but cannot understand why. As memory of Cottle changes, so too does the history that involved him. Relations between the Subterranean and the surface world—already strained in Cottle's reality—are worse in the new timeline. There is a legitimate threat of civil war that Thorndyke must find a way to stop.
Tobias Raikhel also believes the past can be entered and changed. In an unauthorized jump he decides to test his theory by bringing an 1863 Civil War soldier who is about to die into the future. The experiment goes terribly wrong, and several soldiers are brought into the 25th century through a rip in time. As Thorndyke struggles to keep tensions in the Subterranean from exploding, he must also deal with the emerging crisis caused by Raikhel's unauthorized experiment. The cascading effect of an unintended rip in time threatens to destroy the domed city of Washington D.C.