A few short hours after the assassination of President of the United States Abraham Lincoln (Frank McGlynn Sr.), Samuel Mudd (Warner Baxter) gives treatment to a man with a broken leg who shows up at his door. Mudd does not know that the president has been assassinated and the man who he is treating is John Wilkes Booth (Francis McDonald). Mudd is arrested for being an accessory in the assassination and is sent to prison on the Dry Tortugas, described as in the West Indies and referred to in the film as "America's own Devil's Island".