NOTE: This spoiler was sent in by Charmaine then added on by Susan.
The movie opens children playing in front of a large house. A woman is on the telephone, talking about the adoption of Laura, one of the girls playing. There is a scarecrow in the yard that has a creepy burlap head. Flash forward to present day, and Laura (Belen Rueda), her husband Carlos, and their son Simon moving into a new house. They are going to re-open the abandoned house and turn it into a home for handicapped and disabled children. Simon has a couple of imaginary friends, but Laura and husband dismiss them as childhood imagination. The house is near the beach, and Laura takes Simon to a cave near the beach so he can explore it. He disappears, and Laura finds him in the back of the cave whispering, "Do you want to come to my house and play?" Laura tells him to come away, Simon says that he has met a new friend. Laura looks, but there is nothing there. As they walk home, Simon leaves a trail of seashells so that his "new friend" can follow.
We find out that Simon is adopted, and also HIV positive when a "social worker" named Benigna comes to the house to check on Simon. She leaves a file with Laura which contains the HIV and adoption information about Simon. Laura gets offended when Benigna brings up the idea of "new therapies" for Simon, and asks her to leave. Laura locks the file in a drawer in the kitchen.
Simon starts talking about new imaginary friends, and says that he now has 5 new friends. He says that they play a game where they take a valuable thing, then you have to follow clues to find it, and when you find it, you can make a wish. Simon then wants to show Laura some "special coins" that he found at the park. When he opens his box where he kept the coins, they are gone, but he finds the first clue to a treasure hunt around the house. They run around the house following the clues, and Simon finally finds a key and immediately races to the kitchen, and voila, the key opens the drawer which contains his adoption file, and the coins fall out of the file.
Laura and her husband are horrified. They sit down with Simon and explain to him that he must take his medication ever day, otherwise he will get sick and die, but that they are going to take care of him.
That night, Laura is sleeping and she starts hearing a loud banging noise. She starts walking around the house, then eventually goes out to a shed in the backyard. She goes into the shed, and out pops Benigna, who then runs away.
The house is now opening for the kids to arrive. There is a big picnic party, where they hand out masks for people to wear. Simon does not want to go downstairs, and says that he wants to show Laura his friend Tomas's house(one of his imaginary friends). She is rushed and says no. Simon has a temper tantrum, and Laura leaves him upstairs.
Later on, Laura goes to try to find Simon. She is walking around upstairs. As she walks towards a bathroom, a child wearing the burlap mask and one of the old orphanage uniforms comes up behind her. She thinks it is Simon and starts to walk towards the child. Suddenly, the child runs at her and pushes her into the bathroom, and locks the door on her. She eventually gets out, and she runs around the party frantically looking for Simon, but he is nowhere to be found, and there is no trace of him. There is a closet underneath the stairs, and she looks in it. There are a bunch of heavy pipes inside, that fall when she opens the door. She hastily pushes them back in, as she continues her search.
Months go by, and Simon is not found even though there are posters everywhere and police searching. Laura and her husband talk to a police psychologist, who tells them that Benigna was not a social worker, but they will be searching for her as a suspect. One night, Laura wakes up to a loud banging noise in the house. She walks around, searching, and then finds a doll in Simon's bed.
One day, Laura and her husband are driving in a town, and they see Benigna walk across the street in front of them pushing a baby carriage. Laura calls out her name and Benigna turns, and then is struck by a van. A crowd runs to her, Laura runs to the carriage but it just has a doll in it wearing the same burlap mask. Benigna dies (very disgustingly). The police search Benigna's home, and find pics of the orphanage when Laura was there. It turns out that Benigna actually worked at the orphanage, and had a son named Tomas who was deformed, and therefore wore the burlap mask and was hidden away from the other kids. After Laura left, the other kids played a trick on Tomas and he was drowned in the cave by the beach.
Laura realizes the doll is part of the clue game she played earlier in the movie with Simon. She rushes all over the house, and finds the last clue. A door handle. She rushs to the shed….After this, Laura goes to the shed where Benigna had been sneaking around. She finds some old ovens in the back, breaks the locks off, and starts dragging out bags of stuff. She realizes that the bags actually contain the bones and ashes of the kids who had been her friends at the orphanage.
Laura contacts a medium, who comes to the house with a whole setup of electronic gear and people. The medium sits in a chair, and Laura, Carlos, and the police psychologist watch through TV cameras. The medium walks around, then walks to the children's bedroom. She sees a bunch of kids inside, who she says are sick and need help, and that someone poisoned them. The cameras start to go out, so they bring the medium out of the trance. Carlos kicks the medium out of the house, but Laura believes her.
Carlos wants to leave the house, but Laura says that she needs two days to "say goodbye" to the memories. Carlos agrees, and leaves.
Laura then spends a frantic day restoring the orphanage to what it used to look like. She cooks an entire dinner for all the kids, and tries to get them to appear, but they won't. Afterwards, she starts playing a game that they used to play when she was a child. The children slowly appear, then run away. Laura chases a child, who runs to a broom closet under the stairs. Laura goes into the closet, and realizes the door handles are the same as the ones she was looking for. She pulls the door handle out of her pocket and discovers a hidden door. She opens the door, and sees a long creepy dark staircase finds that it is Tomas's room. She goes downstairs, and finds Simon, He is alive and well, but very cold. She picks him up and tells him to close his eyes and forget about the house and the other kids, and Tomas. She wants him to think about what he wants to be when he grows up, etc. When she opens her eyes, she looks down, and realizes the blanket is empty. Instead there is a dead body on the floor next to the staircase. The child has on the old orphanage uniform and the sack mask. She walks over to it and finds Simon dead and decomposing. She looks up at the staircase and sees a piece of the banister is broken. She then realizes what happened. (in flashbacks: Simon asks her to go to Tomas’ little house (the space underneath the stairs), when she is frantically looking for him, she quickly closes the closet door, and jams the heavy pipes against a wall, unknowing she’s locking the hidden door, the banging she hears in the middle of the night is Simon banging to get out.)She then realizes he probably fell down the stairs, broke the banister and died. She carries him upstairs to the children's bedroom, where she then takes a bunch of pills. She falls asleep, then wakes up and Simon is alive. He asks her to stay with them -- Simon and the rest of the orphans -- and take care of them. Laura agrees.
The last scene shows Carlos, back at the house, leaving flowers at a tombstone with the names of Laura, Simon, and the other orphans.