At the narrow passage

Soldier of fortune Eric Mathers has signed on to help in a war among the European nations that resembles what in our timestream is called World War I. But this war continues in the 1970's, and involves an army called the American Colonial Forces—said to be subjects of Britain's King George X! The non-human Kriths, whom Eric worked for, tell him they are altering history to forestall a time-wide catastrophe that their hypertechnology has told them is inevitable. But then the anti-Krith forces Eric encounters tell him his whole rationale for his life as a Krith soldier is false. On Eric's resolution of this dilemma hangs the existence of all civilizations in all timestreams—hangs, in fact, the existence of existence itself. Or so it seems...