In Turtledove's fast-paced fourth Crosstime Traffic novel (after 2005's In High Places
), two teenage protagonists from different versions of the United States meet in Elizabeth, Va., a backwater town in a balkanized North America. Beckie Royer, an inadvertent gunrunner from Los Angeles, accompanies her grandmother and uncle in a car loaded with assault rifles meant for African-American rebels in Virginia. The state, known as a country in this alternate history, is on the brink of a race-related civil war—and a war with Ohio. Into the chaos comes Justin Monroe, a Crosstime Traffic traveler on a trade mission with his mother. Becky and Justin solidify their friendship as the mayhem escalates to biological warfare, and they and their families face ethical and space-time dilemmas. Via sympathetic characters, Turtledove delivers lessons on racism and diplomacy for a young adult audience. (Sept.)