Plot

A mother and daughter, still wounded from a bitter custody dispute, hole up in a run-down apartment building, where they are targeted by the ghost of a former resident.

Dahlia Williams and her daughter Cecelia move into a rundown apartment on New York's Roosevelt Island. She is currently in the midst of divorce proceedings and the apartment, though near an excellent school for her daughter, is all she can afford. From the time she arrives, there are mysterious occurrences and there is a constant drip from the ceiling in the only bedroom. There are also noises coming from the apartment directly above hers, though it would appear to be vacant. Is the apartment haunted or is there a simpler explanation?—garykmcd

Still vulnerable from a traumatic separation and a bitter custody battle with her former husband, Kyle, the troubled and financially hard-pressed single mother, Dahlia, moves into a dilapidated but affordable apartment building with her only child, Ceci. Eager to start afresh, instead, Dahlia still feels the eerie stranglehold of her past, as the damp stain in the ceiling of her dark and dank room seems ready to devour both mother and daughter. Now, little by little, strange occurrences and a creepy imaginary friend begin to blemish Dahlia's beautiful dream of a bright future. Can Dahlia and Ceci escape from the fearsome memory of water?—Nick Riganas

Dahlia Williams is starting a new life; newly separated with a new job and a new apartment, she's determined to put her relationship with her estranged husband behind her and devote herself to raising her daughter, Ceci. But when the strained separation disintegrates into a bitter custody battle, her situation takes a turn for the worse. Her new apartment--dilapidated, cramped, and worn--seems to take on a life of its own. Mysterious noises, persistent leaks of dark water, and strange happenings cause her imagination to run wild, sending her on a puzzling and mystifying pursuit to find out who is behind the endless mind games. As Dahlia frantically searches for the links between the riddles, the dark water seems to close around her. But one thing trumps all others in Dahlia's world: no matter what it is that's out there, she'll stop at nothing to find it.—Sujit R. Varma

Dahlia (Jennifer Connelly) and her daughter Ceci -Cecelia- (Ariel Gade) move to a flat in a condominium because of Dahlia's impending divorce. They go to live to Roosevelt Island, a neighbourhood in New York. Because her soon-to-be-ex-husband Kyle (Dougray Scott) rejects the new school and the new surroundings, it looks that the proceedings for Ceci's custody are turning nasty. The mediators (Bill Buell and Linda Emond) feel that Ceci would be the most damaged person at the end of the divorce, regardless of whom the custody's winner will turn out to be eventually. Dahlia and Ceci live on the ninth floor. Dahlia tries to keep her routines, reading children's books to Ceci before going to bed, taking her to school, etc. However, she keeps on getting splitting headaches and has to take heavy medication. The condo has laundry facilities in the basement and a rude clerk called Veeck (Pete Postlethwaite) who is always complaining about everything but not doing much.

Pretty soon, Dahlia finds herself exhausted. She needs to keep her job to pay her bills, her mother (Elina Löwensohn) disapproves of her life and finds herself worried about Dahlia's psychological strength. When Dahlia first took a look at the flat, she didn't notice that there was a damp stain in a bedroom, but later on, when she and Ceci are already living there, it becomes a huge problem. They also begin to hear strange noises coming from the other side of the walls, The flat is badly-lit, the same as the dilapitated corridors or the dark basement. The clerk promises to call in a plumber.

Two teenaged boys are making mayhem around the flat. They are almost always together and they are considered vandals. One of them even makes a sexual remark to Dahlia when they found her on the basement preparing a washing machine full of clothes. However, they leave , and Dahlia is alone when she turns on the washing machine. It doesn't seem to work properly so she starts another one. She hears strange noises, the water inside the washing machine turns nasty brown and Dahlia thinks that there is a girl inside the washing machine. She pulls the lid until the machine's door opens, but later, when she realises that there is nobody inside, she blames it on a prank played by the two teenaged boys.

Ceci has been unable to make friends in her new school, so she starts playing with her imaginary friend, Natasha. Dahlia tries not to worry, but the weight of the world on her shoulders starts to take its toll. The clerk says that Ceci must have seen/heard Natasha, the little girl who lives in the 10th floor with her father. After the incident in the laudromat, Dahlia sees the red Hello Kittly schoolbag named after Natasha. When Ceci gives it back to the clerk, he just throws it away again.

Jeff Platzer (Tim Roth) is Dahlia's lawyer. He seems to live in his car, all on his own. However, when Dahlia calls him in panic a Sunday evening, he says to her that he is taking his family to the cinema and that he will call on Dahlia the next day. Cue to him, all by himself in the gritty cinema.

Dahlia talks to Ceci and tells her to stop playing with her invisible friend. Later, at school, Ceci is making a drawing of herself and her mother in front of the home. It looks like an invisible force is forcing her to paint on top of the drawing, so that everything becomes a blurred disaster. Ceci gets annoyed and shouts to the invisible energy to stop it. The teacher (Camryn Manheim), sees that Ceci is having a kind of nervous breakdown. She takes Ceci to the bathroom so that she can wash her hands. There, muddy water goes out from all the taps, and Ceci encloses herself within a toilet cubicle. A dark-haired girl in a red coat walks by, splashing on the watery floor.

The teacher (Camryn Manheim) phones Dahlia, who arrives all wet from the heavy rain. She is told that Ceci got dizzy and fainted in the bathroom.

Kyle accuses Dahlia of being unstable and a bad influence for Ceci. Platzer asks Dahlia whether there is anything real in all those accusations, and Dahlia talks about her headaches. Platzer takes the matter on his own hands, as he seems to feel that Dahlia is about to have a breakdown. He phones the owner of the building, Mr Murray (John C. Reilly), who seems really upset when he notices the level of damage made by the water coming from the 10th floor. Murray promises that a plumber will arrive the following day. Next day, the plumber says that the pipes themselves are not the problem, as there was no leakage to begin with.

Dahlia decides to take her fears seriously and investigate the matter. She goes up to the 10th floor, but nobody lives there anymore.

On the 10th floor there lived a family of Russians. They were a disfunctional family: the mother was an alcoholic, but their only young child, Natasha (Perla Harney-Hardine), was nice and welcoming. The mother checked herself into rehab, leaving Natasha with her father. The father returned to Russia, taking for granted that Natasha was with her mother. The child was abandoned by both parents, so one day, when on the rooftop, she walked up the ladder to the big reservoir and drowned in it. It seems that the clerk knew about it, but he refused to do anything about the matter, because after all, it was not his job. Instead, he just stopped taking care of the reservoir, and that was why Dahlia's apartment was getting flooded again and again.

Dahlia peers inside the reservoir. She immediately spots Natasha's corpse. Natasha opens her eyes and tries to take Dahlia inside, but Dahlia leaves the place and phones the police. The police arrest Veeck, but there is no way to prove that either of Natasha's parents killed her, and Veeck is probably only guilty of not having phoned the police when he realised that Natasha was dead.

Once that the ordeal seems to be over, Dahlia talks to Kyle. She proposes to reach an agreement over Ceci's custody and live closer to Kyle. Kyle is overjoyed to hear it. Dahlia intends to leave the condo in only a week... for good.

That night, Dahlia prepares a bath with bubbles for Ceci. Dahlia leaves Ceci in the bath and talks on the phone to her mum. Dahlia is having her bath playing with a blue doll. When Dahlia is about to take Ceci out of the bath the girl is already in the living room, wrapped in a robe. Dahlia starts reading a children's book to her, when suddenly she realises that it is Natasha, not Ceci.

Dahlia has to break down the bathroom door. Natasha is trying to drown Ceci. To save her daughter, Dahlia offers to take care of Natasha forever. The bathroom becomes flooded.

The police are in the building again. They think that Dahlia has committed suicide. Kyle picks Ceci up, and takes her to his home. When they are in the lift, they become stranded. At that moment, the ghost of Dahlia talks to Ceci, combs her hair and tells her that if she has a problem in the future Dahlia would be in the building waiting and that she would help her. Meanhwile, Ceci leaves the building happily, and Dahlia stays to take care of Natasha.