In the summer of 1964, having patiently listened to his grandfather's tales of life in small-town Indiana during the 1920s, the 17- year-old Simon Hughes wondered how the old man could have participated in a mass movement like the Knights of the Ku Klux Klan. Simon then gets drawn into the anti-Vietnam War movement in college and joins the Students for a Democratic Society (SDS). He participates in the student insurrection that assaulted Columbia University in April 1968, when he suffers a life-long injury from club-wielding New York's Finest. Two years later he witnesses from afar the student riots at Ohio State. By 2018, Simon is a retired anthropologist helping his rugby-playing grandson in a dispute with his college. Simon has his own tales of life in the 1960s to tell his grandson, but the two argue continuously. The grandson, Eddie, is a libertarian and Trump supporter, while Simon retains many liberal attitudes and denounces Trump as a demagogue. Simon insists that the Trump base is a mass movement with similarities to both the Indiana Klan of the Twenties and the New York SDS of the Sixties. Now in the digital age, Eddie uses social media to promote his cause and assail his college. Both Simon, much like his grandfather, and Eddie, somewhat like his grandfather, display behavior patterns of true believers and show how rigid ideals can lead to undesirable results on both the Right and Left wings of the American political spectrum over the last 100 years. The Activist is a stand-alone sequel to the novel The Listener (2018).