Summoned by Lucas Davenport to investigate a pair of murders in which the victims are found with lemons in their mouths, Minnesota Bureau of Criminal Apprehension investigator Virgil Flowers struggles to find a connection that could prevent additional killings.

The idyllic lives of civic-minded environmentalists Patty and Walter Berglund come into question when their son moves in with aggressive Republican neighbors, green lawyer Walter takes a job in the coal industry, and go-getter Patty becomes increasingly unstable and enraged.