St. Louis County detective John Martin finds himself pitted against two worthy adversaries. One is the press-dubbed "Nightshade Killer", who has appointed himself judge, jury, and executioner of the underbelly of St. Louis. The other is Jason Benzwyck, an ambitious U.S. Assistant Attorney General who sees the Nightshade Killer as a useful means to a noble end. Nightshade is about three men whose personal struggles blur the lines between revenge, justice and the law.