The shogunate installed by the Tokugawa is abiding order, the people live in peace and in a relative prosperity. However, the dark part of the human heart does not cease to arouse their cupidity: it is the ideal doorway for all demons that, by possessing humans, seek to pass into their world. Exorcising these demons is Jonosuke's mission, the master of keys. Known for being the best locksmith of Edo, Jonosuke uses particular locks to put the wicked spirits under lock and key. With the help of the bewitching O-kin, a divine who uses unorthodox methods, Jonosuke is going to meet during his demon hunt some notables of his time, who will prove to be precious allies when he faces a plot aimed at the upper spheres of State.