Replay (The Gatespace Trilogy)

Rick Harper is part of a research team that stumbles upon the secret of the mysterious Gatespace first seen in PINBALL. When he is diagnosed with a life-threatening illness, he decides to attempt using the technology to influence his own past and try to add years to the time he has to spend with his beloved Stefanie -- with disastrous results. Journeying through the Gatespace to the year 2000, when Stefanie was a senior at Berkeley, Rick encounters a number of challenges that may prevent either one of them from making it home again.