Anna (Emily Browning) has been in a psychiatric institution for ten months, following her suicide attempt after her terminally ill mother died in a boathouse fire. Now, she is being discharged and has no memory of the actual fire, although she is frequently plagued by nightmares from that night.
While packing, Anna is startled by a disturbing, talkative patient who stays in the room across from hers. Shortly after, she leaves with her father, Steven (David Strathairn), a writer who has dedicated his latest book to Anna and her sister.
At home, Anna reunites with her sister, Alex (Arielle Kebbel), with whom she is very close. The sisters stand against Steven's girlfriend Rachel (Elizabeth Banks), who had been their mother's live-in nurse.
Alex criticizes Steven for sleeping with Rachel while the girls' mother was still alive and sick in bed, but her comments fall on deaf ears. Anna describes to Alex how scenes from her dreams have started happening while she is awake. The sisters become convinced that the hallucinations are messages from their mother, telling them that she had been murdered by Rachel.