Lucinda "Luce" Price is sent to Sword and Cross Academy for troubled young teens after she is blamed for the death of a boy named Trevor who perishes in a fire started by mysterious shadows that Luce sees after kissing him. Luce feels cursed, blaming herself for Trevor's death.Upon arriving at her new school, Luce meets various students, including Cameron "Cam," who has taken an interest in her; Arriane Alter, who takes Luce under her wing; Molly Zane, who harasses Luce; Pennyweather "Penn," who befriends Luce; and Daniel, a brooding boy to whom Luce is instantly attracted. She also meets Miss Sophia, a religious studies teacher. During a session, the school psychiatrist tells Lucinda she can leave if she takes antipsychotics.During detention, picking up trash, Luce is almost crushed by a falling statue of an avenging angel. Later, Cam flirts with Luce before inviting her to a party in the woods. At the party, Luce is attracted to Cam, but can't shake the feeling of an deep and unusual connection to Daniel, despite his attempts to brush her off. Molly shows up and proceeds to harass and almost kill Luce before Arriane intervenes. As Luce leaves, she sees the "shadows" again.Luce overhears Miss Sophia telling Daniel that Cam may have been behind the angel statue almost falling on Luce. She expresses fear for Luce because she is unbaptized. The two realize that Luce is listening to them, and Daniel follows Luce outside. They walk together and he admits that during class he was working on a graphic novel. In the story a boy and a girl are in love with each other, but are cursed such that every time they kiss, the girl dies; she then reincarnates, meets the boy (who never ages or changes) 17 years later, and they fall in love and kiss again, only for the cycle to repeat endlessly each 17 years.Cam takes Luce to a club on her birthday and they kiss, only to be violently interrupted by Daniel, who yells that he had told Cam to stay away from Luce, and accuses him of still being "with Lucifer." Luce, flees and tells Penn what happened, confiding that she suspects Cam and she have been reincarnated. Penn and her friend Todd sneak into the library with Luce and search the computer with a facial recognition tool; they discover a photo from 1854 of Daniel and Luce, and Luce again has a flash of memory, seeing herself and Daniel posing for the photo in 1854. As Penn leaves to retrieve the photo from the printer, Luce sees the "shadows" again. Another mysterious fire breaks out; it engulfs the library and kills Todd. Daniel rescues an unconscious Luce from the fire.Later Luce finds Daniel on a roof top, and he reveals that they are the boy and girl from his graphic novel story. Daniel further reveals that he is a fallen angel, which explains his immortality. The two kiss, but Cam appears, telling Luce that because she has not been baptized, Lucifer will come for her. He tries to convince Luce to pick him instead of Daniel, but Daniel whisks Luce away and takes her to Miss Sophia, leaving to fight Cam and stop Lucifer from coming for Luce.As the two fight, Cam reveals that he was not the one behind Luce's murders; meanwhile, Sophia kills Penn. Luce screams, which brings Daniel to her aid, to protect her from Miss Sophia, who was actually the one trying to kill Luce. Miss Sophia justifies her murders by explaining that, with Luce gone, Daniel would have been forced to choose a side and order would have been restored. The shadows show up behind Miss Sophia as she is talking and consume her.Daniel explains to a shaken Luce that her being unbaptized would make her next death permanent; Sophia thought this would cause Daniel to choose Heaven. He tells her that Lucifer will indeed come for her, and that he must take her somewhere safe. They declare their love for each other as they leave to find safe haven from Lucifer.