Crosstime Traffic is a company, 130 or so years in our future, which has developed the means to travel sideways in time--that is to say, to travel to might-have-beens, presents that are parallel to, but different from, our own. In addition to doing whatever a company such as this might do to make money, Crosstime Traffic awards grants to historians and other researchers to visit various alternate presents to figure out what went wrong (or right).
An intriguing premise, and one upon which the extraordinarily prolific Turtledove has based one of his many uber-creative series. In this installment, a pair of professors from UCLA and their daughter are conducting research in an alternate in which a nuclear conflict in 1967 decimated the world as we know it. As The Valley-Westside War opens troops from the Valley are preparing to march on the Westside, which has blocked access from the north in an attempt to solidify its holdings throughout the South Bay area. Technological development having come to a crashing halt when nuclear fire rained from the sky, soldiers on both sides are armed with bows and arrows, old-fashioned muskets, and, in rare cases, found--and none-too-reliable--weapons from the Old Time.
The novel alternates between the points of view of a young solder in the Valley army, Dan, and Liz, the daughter of the two visiting historians. Turtledove has done a beautiful job of working out how different things would be were technology and globalization to have ceased before man walked on the moon. The tension in the story, such as it is, comes from Dan's attempts both to gain the attentions of and figure out Liz, and Liz's own attempts to avoid young Dan and hide her true origins.
Unfortunately, although the premise, as noted above, is intriguing and the details well-thought out and fascinating, the story itself is juvenile and the writing barely workmanlike. I wouldn't not read another of these novels if it came my way, but I certainly wouldn't seek it out.