A few short hours after the assassination of President Abraham Lincoln (Frank McGlynn Sr.), Dr. Samuel Mudd (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". After a period of ill treatment due to his notoriety, his skills as a doctor are requested by the Commandant of the prison. The island has been in the grip of a yellow fever epidemic and the official prison doctor has fallen ill. Dr. Mudd takes charge with the blessing of the Commandant and the cooperation of the soldier guards, and the yellow jack epidemic subsides. In the end he receives a pardon and is allowed to return home.