Ramira [Alexandra Jiménez] works as maid and nanny to Laura [Silvia Abril] and her children: Simeón [Óscar Lara] and Ofendia [Laia Alda]. Unfortunately, Ramira kills the boy within minutes of meeting him, when she insists he goes out into the sun for his photodermatitis, a cruel accident that traps the family in a tangle of fear and guilt.
Ramira tries to hide her crime and lies to Laura about Simeón's death. She then meets Laura's brother Pedro [Carlos Areces] San Antón, who is paraplegic like Ramón Sampedro (or at least claims to be). The house is suddenly alive with supernatural visitors, including a Fairy [Michelle Jenner] and a Faun [Joaquín Reyes], many of whom fall foul of the psychotic Ofendia [Laia Alda]. One visitor, Maligna Escobero [Teresa Lozano], is especially terrifying and subtly pressures Laura to make Simeón wear a sack mask to protect him from the sun.
Ramira enlists the help of Jose [Joselito], who convincingly tells Laura that he is Simeón, despite being a middle‑aged man. In the chaos, Ramira inadvertently kills her alcoholic, unemployed husband Antonio [Luis Zahera] and declares her love for Pedro, further muddying the truth inside the walls of the house.
Laura grows suspicious when Simeón does not appear even on his birthday, and she chases a figure wearing a sack mask through the house. After hearing a telltale party horn, she finds him in the woods outside her home, only to discover her long‑lost husband Diego [Eduardo Gómez]. After a brief, tense reunion, Diego leaves again.
Pedro insists he cannot leave his sister until he learns the truth about Simeón. Ramira returns to her village to seek help from a local mystic. They arrive just in time to witness Maligna Escobero die in a fatal accident, not even Doctor Nielsen [Leslie Nielsen] can save her.
With local medium Gerarda unable to help, the group returns home. Pedro tries to end his life, but the process is complicated by the difficult director he finds to make his goodbye video.
Ramira rushes to Pedro's bedside after learning he has taken cyanide, and is joined by the Fairy [Michelle Jenner] and the Faun [Joaquín Reyes]. The Faun explains the convoluted reality: Pedro exists in the year 3028 and his current reality is all a dream. He must choose between staying with Ramira, or waking up in the future. He chooses to stay with Ramira. When the Faun turns violent, Ramira mesmerises him with a song and pushes him off the building. He falls into infinity, but Pedro concentrates and controls his dream world, flying to the top of the building to embrace Ramira.
Meanwhile, Laura remains convinced Simeón is nearby. She finds a trail of phallic toys around the house and is eventually visited by the boy in the sack mask, who leads her to a hole in the wall. It turns out to be Ofendia, who leads her to Simeón's mutilated remains. Distraught, Laura swallows a handful of pills—realizing they are laxatives—and is visited by Pedro, who tells her that if she concentrates, she can bring Simeón back. Simeón is revived, and Laura opens the doors of the house, telling him he has nothing to fear. With his mother otherwise occupied in the bathroom, Simeón tries to leave the house with Ramira and Pedro, although not all of him makes it out.
