Dahlia Williams is going through a bitter custody battle for her daughter Ceci. Amid this tumultuous time, she decides to move to a dilapidated and eerie apartment building on Roosevelt Island, New York, seeking a fresh start for herself and her daughter. The building, and particularly their new apartment, feels unwelcoming, with persistent leaks of dark water from the ceiling adding to their discomfort. The environment is hostile, not just physically but emotionally, as Ceci starts mentioning an imaginary friend, adding to Dahlia's growing concern and anxiety about their decision to move there.

As Dahlia delves deeper into the mystery of the leaking water and the history of the apartment building, she discovers unsettling truths. The dark water seems to be more than just a physical issue, hinting at the building’s dark past. Her investigation leads her to uncover the story of a young girl who once lived in the building and vanished under mysterious circumstances. As she becomes increasingly obsessed with finding out what happened, Dahlia's own past and psychological state come into question, intertwining with the eerie occurrences in the apartment, leading to a chilling revelation that threatens the safety and sanity of both mother and daughter.