At the Narrow Passage (The Timeliner Trilogy Book One)

Plot

From far in the future comes a hideous warning of destruction. But the message is not clear, and the result is a mad scramble to change the present -- all possible presents -- in order to avoid the future. For the recipients of the message are not humans but Kirths, lizardlike beings from a parallel Timeline. Using machines that move sideways in time, a band of dedicated mercenaries and Kirth leaders cut a wide swath through countless Timelines. It is a brutal and bloody struggle that has no end -- until one of their strongest fighters begins to ask questions the Kirths would rather not answer.