Virtual Mode — Piers Anthony

Colene does not know what to think of the stranger she has rescued. Darius tells her he has traveled from his reality to find her. In proving to Colene that other worlds do exist, he uses up the power of the artifact that would allow them to travel back to his universe. They must try a slower, more dangerous method: the creation of a four-dimensional universe. Darius picks five anchor points in five different universes to set up a skew path, a Virtual Mode, on which the anchors can walk. Thus begins a tale of romance, danger, adventure, and intrigue as the two travel through a myriad of alternate realities where anything is possible.