I struggled with this book. Thousands of years in the future humanity consists of the Changed; humans who can use their will to move things and a few with the ability to navigate the rivers of time - the timeswimmers. Their numbers however have fallen to dangerously low levels and they require wild genetic input from humans in the past and a pair of Changed make the journey, hopping on islands of stable time, to our present to kidnap a group of young humans, which includes Luke Tabor and his girlfriend. In the far future (or Far Islands) the present-day males are used for sperm and the females forcibly impregnated but they have also landed in a conflict between powerfully opposed groups of Changed, some of whom want a future off Earth. F. M. Busby has posited a neat conceit - the time river - then proceeded to muddy it so completely that the plot gets a bit confused and hard to follow (let alone believe). It would have benefitted from a serious prune, and my memories of Busby’s earlier work assure me that he has written much better than this.