The Shadow Matrix

Blurb

The Shadow Matrix is a science fiction novel by Marion Zimmer Bradley and Adrienne Martine-Barnes in the Darkover series. It was first published by in hardcover by DAW Books in 1996. Since the book involves time travel, it falls in both the Darkover time periods that the author called "Against the Terrans: The Second Age" and in the Ages of Chaos.
In terms of Darkover's timeline, the book starts place about a year after Exile's Song, and is a continuation of that story.