A man finds that some of his dreams - those he calls 'effective' - are changing the world, not in small ways but comprehensively, by rewriting the entire course of history (human at the very least, seemingly planetary also, and very possibly beyond even that if the iterating appearances of the aliens are anything to go by - although the strange insight they appear to possess into this effective dreaming is a wrinkle suggesting a different character to their subjectivity) to create a new present-day, with no one other than Orr himself being aware of the replacement. The novel moves through its scenario and its ideas and implications without any unnecessary texture, as Orr's treating psych Haber discovers what is happening and seeks to use the phenomenon to better the world, and successive attempts succeed or fail to lesser or sometimes very much greater extents. It's an older style of sci fi I suppose, and it's effective.
