The Valley-Westside War: Crosstime Traffic, cartea 6

Usually Crosstime Traffic concerns itself with trade. Our world owns the secret of travel between parallel continuums, and we mean to use it to trade for much-needed resources with the worlds next door. Preferably without letting them know about any of that parallel-worlds stuff.

But there's one parallel world that's different. In it, the atomic war broke out in 1967, at the height of the Summer of Love. Now, Crosstime Traffic has been given a different sort of mission: find out what on earth, or on the many earths, went wrong, in The Valley-Westside War, the sixth book in Harry Turtledove's parallel adventure series.