Lone-wolf terrorism is a growing concern for security and a puzzle for social science. We describe two very different cases of lone-wolf terrorism: a meek secretary in nineteenth century Russia who attacks a prison governor, and a criminal turned anti-abortion crusader in twenty-first century USA. These cases point to two explanations of how normal individuals can overcome the “free-rider problem” to undertake solo violence for a political cause. Strong Reciprocity establishes an evolutionary basis for human willingness to punish moral transgressors, even when the transgression is against someone else. Group Identification can enable self-sacrifice for the welfare of others, including actions against those who threaten the group. Discussion suggests that ideology, ideas of justice, and empathy may be more important for solo political action than for action embedded in radical groups or terrorist organizations.