The Valley-Westside War
Harry Turtledove
 The Mendoza family, funded by a Crosstime Traffic grant and disguised as traders, return to postwar Earth to learn who initiated the hostilities. Liz Mendoza frequently visits the UCLA library to analyze the period books and magazines, searching for insight and reasons for the conflict. It is on her regular trips to the library that she meets Dan, a Valley soldier whom she initially considers dull and dumb. Dan, however, is not as unschooled and ignorant as Liz thinks, and, although he is attracted to her, he has his misgivings about the Mendozas. His suspicions are confirmed, and he blows their cover and causes them to return to their own time alternate, but not before he asks why someone from a different time, who has the knowledge and expertise to help Earth recover from its postwar havoc, does nothing.