The air of celebration surrounding fifteen-year-old Oz Vessalius's coming-of-age ceremony quickly turns to horror when he is condemned for a sin about which he knows nothing. He is thrown into an eternal, inescapable prison known as the Abyss from which there is no escape.
There, he meets a young girl named Alice, who is not what she seems. Now that the relentless cogs of fate have begun to turn, do they lead only to crushing despair for Oz, or is there some shred of hope for him to grasp on to?
Oz Vessalius is upon his Coming-of-Age ceremony to one day become the next head of the Vessalius dukedom. With his uncle Oscar's consent, he, his servant Gilbert, and little sister Ada go out to explore the mansion the ceremony is being held at. Oscar threatens that if the three are not back soon, he'd send the "Messenger of the Abyss" on them. Oz simply replies with a laugh, saying he doesn't believe in such stories anymore.
Upon Ada's questioning, Gilbert and Oz explain that the Abyss is a dark prison were people who've committed terrible sins and will never be able to get out once you are sent there by a Shinigami. Then Oz then gives Gil a box that Oscar gave him earlier that contains a formal uniform. Oz wishes Gil to be a part of the ceremony too, not as his servant, but his friend, despite the latter's protest.
At the before-ceremony party, Oz meets Sharon Rainsworth, the granddaughter of Duchess Rainsworth. She claims to have some in her mother's place because she fell ill. Oz immediately takes a liking to her because she is so cute. But because she's not yet fifteen, she cannot stay at the party, so before she leaves Sharon tells him a cryptic warning that many people will approach him from then on for their own gain, and that all would see his father in him. She tells him not to forget those who support him, and she leaves alongside a mysterious man that bows to Oz wordlessly.
The Ceremony begins as Oscar blesses him with a baptismal sword and then Oz recites his vows before the "Clock Tower of Silence." He's pleased when he sees that Gil has made it to the ceremony and then begins his vows. But just as Oz finishes them, the minute hand of the clock shockingly moves and chimes midnight.
Oz is running through a dark place, his clothes tattered and dirty. He finally stops, thinking about what has happened to him. With a look around, Oz incredulously wonders if he is really in Abyss, as the place is swarming with broken furniture and toys.
A monster appears behind Oz and pins him to the ground, but before it can do anything, its destoryed...by the very same girl Oz has been seeing. She explains that the monster was a Chain - a being born from the Abyss - and that she was one too, the "B. Rabbit." Oz asks if Chains always try to kill people, just like she did to him in the dream. She seems not to know what he's talking about, saying the first time they met was at the ceremony. The girl says she gives him permission to call her by her name, "Alice," and tells him that she's just using him for her own purpose: to get out of the Abyss for good. She can't do this herself because of a limit to her power; that's why she needs to form a Contract with a human so that she can access all her power. Oz considers her offer and is about to agree...
Oz wakes up to find someone sitting next to where he lay. He reaches out a hand and tentatively murmurs Gil's name, making the person turn. Although he looks similar to Gil, the person is a grown man. The man gets up, and putting on a black jacket, announces to Break that Oz is awake. Break, sitting beside a sleeping Sharon, happily greets a confused Oz. He explains to Oz that they were in one of the Rainsworth's mansions, that they took him under their protection - and that Oz was home, back in the real world.
Oz changes into new, more casual clothes, to which Break complimented that he looked good in them. Break then introduces himself as a servant to the Rainsworth family household, also introducing his doll, Emily, who cackles at Oz, much to his shock. Break, offering Oz a seat, proceeds to tell Oz that he heard all about the chaos at his Coming of Age ceremony from Gil and through this, Oz learns that everyone at the ceremony is safe: his uncle, his sister, and his servant. Break however, told him that he'd now like to know what happened after Oz was banished to the Abyss. After Oz explains his tale, Emily and Break joked on how they were never needed. Break then asks Oz where the B-Rabbit was at the moment, but Oz confesses he doesn't know since when he came to, she was gone. All he knows is that she approached him in the first place because of the watch's melody.