Professor Andrew Picken's scholarly knowledge of Detroit's violent past puts him in present danger when a wild-eyed stranger barges into his class and asks for his help in solving a ninety-year-old mystery. The man introduces himself as Murphy - no first name. Murphy is a retired Detroit cop who once served as an Army Ranger in Vietnam and is now a private detective. He is old, fat and sloppy, a heavy drinker, a self-proclaimed Buddhist and a legend in law enforcement circles for reasons good and bad. He asks Pickens, who has written a book detailing the history of criminal gangs in Detroit, for help solving a hate crime involving the Black Legion, a white supremacist group that terrorized the city in the 1930s. Pickens is reluctant to get involved until Murphy reveals a fresh gunshot wound he received on the way to the lecture hall. Pickens is a former investigative reporter who now teaches history at Wayne State University in Detroit. The reason for his career change unfolds as the story proceeds: after receiving death threats for his stories about contemporary criminals he decided it was safer to write about criminals of the past. Pickens takes Murphy to a nearby hospital, where he meets Baxter Fineman, a professor emeritus of law at Wayne State and the client Murphy is working for. Fineman is an African American who wants to prove that his grandfather did not abandon his family in 1931, but instead was murdered by the Black Legion. Pickens is reluctant to get involved but agrees to meet with the next day to learn more. At the meeting Murphy explains that he has uncovered a modern-day version of the Black Legion, and that they are pursuing a valuable artifact once owned by Henry Ford that they believe will help them finance their hate crimes. He is certain a member of this new Black Legion shot him on the way to Pickens' class. Fineman then shows Pickens a series of cryptic letters his grandfather wrote to his grandmother around the time he disappeared. The first has a single sentence written at the top: If I don't come back go to Hell. Fineman and Murphy want Pickens to use his knowledge of Detroit gang history to help them uncover the facts. He is about to turn them down when he remembers an old news article he came across doing research for his book in the university archives. He changes his mind and agrees to provide at least some initial help. That night Pickens rehearses with the old-timers from his late father's bluegrass band who he has helped reunite. They have recently added a younger woman who is obviously attracted to him, but once again he is reluctant to get involved. The information Pickens uncovers in the archives begins to explain what happened about Fineman's grandfather and the lost artifact. An elaborate, clue-filled treasure hunts takes Murphy and Pickens to Hell, Michigan, where they dig up a grave and uncover another clue that leads all three men to Paradise, Michigan. At each step along the way they experience an escalating series of violent encounters as the Black Legion tries to stop them. After each attack Pickens wavers on the edge of quitting, until a trip down a well and a near-fatal bomb explosion at a log cabin in Paradise steels his resolve. The clue in the well leads them to the Masonic Temple in Detroit, where Theater Bizarre, one of the strangest Halloween parties in the world, is underway. Surrounded by vampires, zombies and killer clowns, Pickens goes after the artifact, which is hidden in a wall. The trained Black Legion killer who has been trying to murder him is also there looking for the artifact. The nightmarish evening ends with Pickens disarming and killing him. Pickens recovers the artifact, begins a relationship with the woman in the band, and has a new commitment to engaging with life and making the world a better place. The novels end with the Bluegrass Devils of Detroit playing their first gig together at the Hell Hole Bar in Hell, Michigan.