SHORT VERSION: (Thanks Rick)!
Casey (Odette Yustman) is haunted by the ghost of a young boy which claims to be her unborn twin brother.
The boy is not her brother, but a demon which has haunted her family for decades, starting with Casey's grandmother while she was in a Nazi concentration camp.
An exorcism finally drives the spirit away, but not before it kills several people including Casey's boyfriend. Casey later goes to a doctor and finds out that she is pregnant with twins. It's suggested that the demon will try to use the twins to come into this world.
LONG VERSION: (Thanks Melissa S!)
The movie opens with Casey Bell, (Odette Yutsman), on a cell phone, telling her best friend all about a nightmare She's been having about a little boy and a mean dog wearing a mask. Casey is baby sitting the neighbors kids, a baby girl and a creepy little boy. Casey hears a noise upstairs and goes upstairs to find the little boy holding a mirror over the babies face and saying "Jumby wants to be born". Then the little boy hits Casey in the face. (Later Casey's friend tells her that a baby shouldn't see it's reflection for its first year of life because if it does the baby will die.)
Casey gets upset and over the next couple days strange things happen to her. Her brown eyes start to turn blue, a doctor asks her if she's a twin, she says no but then goes to her dad's work and asks him, he says yes, she had a twin brother who died in the womb because Casey's cord wrapped around his neck. Casey gets more upset, asks her dad if the death of her brother was what made her mother hang herself? He says NO.
Casey starts seeing things. Big ant looking bugs the size of rats, the little boy is every where, she has more bad dreams, the neighbors baby dies, Casey goes to a night club with her friends and boyfriend and sees the "ghost" boy, she throws up and gets locked in the restroom and attacked by the ant creatures.
Casey and her boyfriend find old home movies and a photo of Casey's mom while she was pregnant. Her mother was standing by a mirror in the photo and the "ghost boy" was in the picture, reflected in the mirror. Casey learns that her mom was adopted and that shortly before her mom's suicide she had found her birth mother. Casey tracks down her grandmother who at first rejects her and then calls her later to explain why.
Casey's grandma was a twin, the "ghost boy" was her brother. The twins were victims of the Holocaust. Hitler's men were doing experiments on twins to learn about DNA. The "ghost boy" had died during an experiment on eye color after they had injected something into his eyes, turning them blue. Two days after the boy died he came back, his sister knew it wasn't really her brother but a demon, so she killed him and he's been haunting her bloodline ever since. The boy is what drove Casey's mom insane. Casey tries to figure out why the boy is suddenly after her now and had not come after her before.
Casey's grandma tells her to seek out a minister who can help her do an exorcism. Casey steals an exorcism book from the library, finds the minister, he agrees to translate the book.
That night Casey's grandma is murdered in the old folks home by the "ghost boy", of course there are a few scary images as the ghost chases her.
Casey's best friend tries to go see Casey and hits the neighbor boy, that Casey had been babysitting, with her car. The boy is unharmed but warns the friend not to help Casey because the "ghost boy" will kill her if she does. The woman ignores the boys warnings.
The best friend and Casey go to see Casey's grandma and find out she is dead and has left her a letter, telling her she must finish what has been started. Casey goes home and talks to her best friend using a web cam. Casey sees on the web cam that something is wrong at her friends house. She calls her boyfriend and they rush over. The ghost boy possesses the neighbor boy Casey baby sat, the boy goes to Casey's best friends house and stabs her to death. The ghost leaves the boys body and goes into the dead body of the friend just as Casey and her boyfriend show up to save the friend, they are to late.
Casey and her boyfriend talk to the minister who oddly has another minister and ten other people who are willing to do the exorcism. They all meet at the abandoned hospital where Casey's mom had hung herself several years earlier. They strap Casey to a gurney and then they start blowing a giant horn to provoke the ghost. They start the ritual and the ghost gets angry tossing the volunteers around killing them. Casey gets off the stretcher and runs with her boyfriend. The ghost jumps from one body to another finally landing in Casey's boyfriend. Most of the minister's friends are dead. The minister and Casey finish the exorcism yelling the final words at her boyfriend and he is launched off the balcony and falls to the marble floor; the ghost is gone. The boyfriend dies in Casey's arms.
The screen fades to black and then it shows Casey getting an ultra sound; she is pregnant with her dead boyfriends twins.