William Twining is the orphaned son of the Twining family, one of Britain's oldest and most noble lines. When he learns his tuition has yet to be paid, he returns home to find the family in crisis - his uncle, inheritor of the entire estate, has gone bankrupt and disappeared. Searching the house for anything that might help him pay for school, William stumbles upon a hidden basement room and inadvertently summons a demon, Dantalion, who informs him he is the "Elector;" the one and only person who can appoint an interim leader of Hell.
Dantalion, one of the many candidates for Lucifer's throne, decides to live in the human world an attend William's school and lobby the young noble to choose him as Hell's ruler, but he gets more than he bargained for when William's friend Isaac accidentally summons one of his competitors!
Sytry remains at the academy to try and convince William to choose him over Dantalion. Fed up with the situation, William orders Dantalion to leave and never come back. Will he regret his decision when the academy is besieged with ghosts that very night?
William's butler Kevin has come to the academy to act as a priest. Shocked by Kevin's suddenly cold demeanor, William decides to skip boating lessons. On his way back to the dorms, he notices the Head Boy, Nathan, acting suspiciously around the dormitory mother's room. Combined with Dantalion's unease around Nathan, it seems there is more to him than meets the eye.
Even after Camio reveals himself, William remains concerned only with his grades and tuition and tries to distance himself from the demons and their political war. Unfortunately, he soon finds himself roped into another problem when the Headmaster asks him to find the source of a mysterious singing voice that's been disturbing students late at night.
It's family visiting day at the academy, but with his parents long dead and Kevin treating him like a stranger, William is feeling down. His mood quickly changes when the father of fellow prefect Swallow invites him to dinner, and the boy himself insists he wants William to "meet my parents."
Dantalion and Sytry must return to the netherworld when the four Kings of Hell come together for their annual summit. None among the crowd realize that the Grand Duke Baalberith has secretly sent a horde of demons to the human world to kill William, the Elector who inherited King Solomon's soul.
The archangel Michael appears before Kevin, informing him that he has come down from Heaven to judge the inheritor of Solomon's soul. For his part, William is busy defending his position as top in the class from a student named Elliot.
Michael moves to deal with William once and for all, while Dantaltion and the other demons are called back to repel an attack by Heaven's armies. Leading the charge is none other than Jeanne d'Arc, the unrequited love of Gilles de Rais. With Heaven closing in, it seems William is doomed to Heaven's ecstasy...or death.
Hoping to win the prize for best event at Stradford's school festival, Wlliam orchestrates a culinary showdown between Dantalion and Sytry's respective butlers, Baphomet and Leonard.
In light of Heaven's invasion, the Four Kings of Hell mutually agree that the Elector must be protected at all costs. But when William reveals he now has Solomon's ring in his posession, Baalberith has a change of heart…
The dispute over Lucifer's successor finally awakens Solomon's soul, but Dantalion is the one demon he does not remember. Dantalion is resolves not to let the same tragedy happen again, but can he still save William's soul?