Falsely accused, Lucinda Price is sent to a strange reform school where she meets intriguing Daniel, who believes they've met before, and Cam, who claims to know why she's really there. Unsettled, Luce doubts her sanity and tries to flee.

Reeling from her punishment in solitary and troubled by the Shadows, Luce questions her memory of what happened when she tried to run away. Disturbing memories of hurting Cam haunt her and she sets out to retrieve his medical records to find the truth. Daniel, shattered from his own severe punishment, refuses to assist with Luce's plan, but when she gets into trouble, he steps in. Luce manages to get the medical data out of the facility for decryption, but she's left with a single photograph that shocks-it's a glimpse into Daniel's impossible past.

Cassie, the only person to escape Sword and Cross, is confronted by a nightmarish creature. Luce suspects that Howson is controlling their memories-she steals photographs of her and other residents undergoing a medical procedure that they don't remember having. The residents are sent on a hike while Howson orders Cassie be brought to Sword and Cross. Daniel and Luce grow closer trying to work out their hidden past. When something attacks Luce in the lake, Luce and Daniel are taken to the medical bay-they break into a restricted room and are shocked by what they find.

Howson organises the capture of the creature that attacked Luce in the lake and interrogates it-establishing it is an Outcast, an ancient creature with a hive mind. Luce comforts Daniel over his grief for his friend, Cassie while they await the return of the decrypted medical files. Learning that the files will be returned during an evening activity, Luce tries to work out how to sneak away to collect them. Salvation comes when Penn's father turns up at the facility, looking for answers about his 'dead' daughter. Luce and Daniel retrieve their files, but the content turns their world upside down.

Daniel has been in the facility for over twenty years - but hasn't aged. It is the same story for the other residents - and worse, Howson has been running experiments on them, suppressing their memories to keep them trapped. Luce and Daniel plan to break out of the facility to alert the authorities, but their escape is cut short - Howson has been tipped off. As they try to work out who betrayed them, the Outcast escapes and injures Daniel, chasing them through the facility. Desperate to save Daniel, Luce tries to find sanctuary but discovers a shocking secret instead.

Miss Miriam initiates a desperate hunt for the Outcast while Howson tries to save Daniel's life. Luce, Cam and the other residents try to make their way to safety, but the creature pursues them, leaving a trail of death in its wake. Luce discovers the identity of the person who leaked their escape attempt to Howson. Meanwhile, Daniel fades on the operating table; unconscious, he relives his time with Luce in a past life. As life slips away from Daniel, Luce fights her way back to the medical bay to reach him and save his life.

Miss Miriam reveals some of Sword and Cross's secrets to the residents. As they reel from the revelations, Luce has her own issues. Daniel has rejected her, worried that she will be cursed to die an early death if she stays with him. Furthermore, the Shadows have shown her a vision of Penn's death, and she struggles to figure out what it means. When Luce and Daniel learn that Penn is planning to leave to find her father-Luce talks her into staying for her own safety. But Penn breaks her promise.

Mourning Penn's death, Luce believes it was murder. The residents work together to get answers. Daniel confronts Miss Miriam, Cam confronts Howson, and Luce confronts Miss Sophia, who traps Luce in the library and sets it ablaze. Daniel rushes to help Luce escape, and the pair are reconciled. But Miss Sophia won't give up; she kidnaps Luce and drags her to a sacred altar in the woods. With Outcasts overrunning the facility, Daniel and the other residents fight their way to the woods to find Luce and become trapped in an epic showdown.