Story Structure — 5 Plot Phases
The Phone Across Time
Seo-yeon discovers a phone linking her home to the same house in 1999. She and Young-sook learn about each other's troubled relationships with their mothers.
Key Events
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A Call from the Past — Seo-yeon receives a distressed call from a woman living in the same house in 1999. Characters: Seo-yeon, Young-sook
Location: Seo-yeon's childhood home
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Two Eras Connected — The women establish that the phone connects them across twenty years. Characters: Seo-yeon, Young-sook
Location: The same house in 1999 and 2019
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Shared Family Pain — They discuss their troubled relationships with their mothers. Characters: Seo-yeon, Young-sook
Location: The connected house
A Past Rewritten
Young-sook prevents the fire that killed Seo-yeon's father, changing the present for the better. Seo-yeon later warns her about her mother's plan, but Young-sook's survival leads to further violence.
Key Events
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The Fire Is Prevented — Young-sook uses Seo-yeon's information to prevent the fire that killed Seo-yeon's father. Characters: Seo-yeon, Young-sook
Location: The house in 1999
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A Better Present — Seo-yeon's reality changes; her parents are alive and the house is lavish. Characters: Seo-yeon, Young-sook
Location: The house in 2019
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A Warning of Death — Seo-yeon learns Young-sook was supposed to die and warns her about the danger. Characters: Seo-yeon, Young-sook
Location: The house in 1999 and 2019
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Young-sook Kills Her Mother — After being warned of her mother's plan, Young-sook kills her mother. Characters: Young-sook
Location: The house in 1999
The Killer's Leverage
Young-sook becomes a serial killer, and Seo-yeon realizes the past is affecting present-day events. A careless phone conversation gives Young-sook information about her future arrest.
Key Events
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The Killer's Victims Disappear — Young-sook becomes a serial killer, and her victims' disappearance reveals the changing past to Seo-yeon. Characters: Seo-yeon, Young-sook
Location: The house in 2019
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A Fatal Hint — Seo-yeon inadvertently reveals that Young-sook will be arrested. Characters: Seo-yeon, Young-sook
Location: The connected house
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The Child Is Taken — Young-sook kills Seo-yeon's father and takes eight-year-old Seo-yeon captive. Characters: Young-sook, Seo-yeon
Location: The house in 1999
The Notebook and the Truth
Young-sook takes young Seo-yeon captive after killing her father. Adult Seo-yeon seeks the police notebook, and Young-sook reveals that Seo-yeon caused the original fire.
Key Events
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The Notebook Changes — Seo-yeon searches for arrest information as Young-sook threatens Eun-ae; the notebook reveals Seo-yeon caused the original fire. Characters: Seo-yeon, Young-sook, Eun-ae
Location: The house and local police station
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The Original Fire Revealed — Young-sook reveals Seo-yeon had lied about Eun-ae causing the fire. Characters: Seo-yeon, Young-sook
Location: The connected house
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A Warning for Eun-ae — Seo-yeon gives Young-sook the correct information, then warns 1999 Eun-ae about her. Characters: Seo-yeon, Eun-ae
Location: The house in 1999
A Rescue Rewritten
Seo-yeon warns Eun-ae as Young-sook pursues her in 1999 and an older Young-sook pursues Seo-yeon in 2019. The timeline changes and mother and daughter reunite, before a mid-credit reversal shows Seo-yeon captive again.
Key Events
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The House Pursuit — Young-sook kills a police officer and chases Eun-ae as an older Young-sook chases Seo-yeon. Characters: Seo-yeon, Young-sook, Eun-ae
Location: The house in 1999 and 2019
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A Changed Reunion — Eun-ae seemingly sacrifices herself; the timeline changes and Seo-yeon reunites with her surviving mother. Characters: Seo-yeon, Eun-ae, Young-sook
Location: The derelict house
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The Call Reverses — An older Young-sook warns her younger self; adult Seo-yeon is shown captive again. Characters: Seo-yeon, Young-sook
Location: The torture room