Elizabeth, portrayed by Abbey Lee, is a newlywed who arrives at an extravagant home with her husband, Henry, played by Ciarán Hinds, on their wedding day. The vast estate is only attended by two staff members: the mysterious Claire, acted by Carla Gugino, and the blind Oliver, portrayed by Matthew Beard. Initially, life seems perfect, and Henry tells Elizabeth she can explore any part of the house except for one locked room located in the basement.
As Elizabeth indulges in the luxurious amenities of the home, her curiosity grows, eventually leading her to break the one rule instilled by Henry. Upon unlocking the forbidden room, she stumbles upon remarkable but disturbing clones of herself. Terrified, she flees the room, leaving the door ajar. When Henry returns and realizes her betrayal, he brutally kills Elizabeth. Claire and Oliver assist him in concealing her body in a shallow grave within the estate.
Six weeks later, another woman named Elizabeth arrives at the same home on her wedding day, mirroring the earlier events. This new Elizabeth, however, is more cunning and manages to take Henry’s life before he can do the same to her. Oliver and Claire quickly uncover her deception; Claire suffers a heart attack and is rushed to the hospital. Alone with the new Elizabeth, Oliver blackmails her to ensure her silence, insisting she would face arrest for Henry’s murder if she tried to leave. He escalates his threats by murdering a cop who came to check on a distress call from Elizabeth, claiming that it was actually Claire who made the call.
To uncover the deeper truths of the mysteries surrounding the house, Oliver confines Elizabeth and compels her to read Claire's diary. Within its pages, she uncovers the tragic backstory of Henry and Claire, who were once brilliant scientists attempting to clone Henry’s deceased wife, also named Elizabeth, who tragically died due to a genetic defect. Although the cloning process initially encounters setbacks, attempts yield success, resulting in Elizabeth clones who can retain some memories of the original but remain innocent and naive.
The diary reveals Claire's suspicions regarding Oliver being Henry's clone. When Elizabeth shares this with Oliver, he reveals a traumatic childhood incident where Henry blinded him out of jealousy. Oliver is nearing the completion of a sixth clone. After Elizabeth seduces him and lowers his defenses, a new clone unexpectedly appears with a shotgun. In an accidental twist of fate, this new clone mistakenly shoots Oliver, leading to chaos as Elizabeth 5 attempts to escape but eventually meets her end, whispering a message to the latest clone just before she is shot.
This new Elizabeth uncovers more about the past when she reads the journal detailing Henry and Claire's history and their grotesque experiments. Flashbacks unfold, revealing their conversations about the cloning process and Henry's disturbing intentions to recreate and then harm the duplicates. He manipulates Claire into agreeing to a new contract that would allow her to oversee his work perpetually.
After her recovery, Claire returns home, and the final Elizabeth clone entrusts her with the diary, urging her to use her knowledge for good. The clone then departs, embarking on a journey to assert her own existence beyond the shadows of a past shrouded in tragedy.
