Four siblings investigate the events that led to the murder of their father and disappearance of their nanny, Mary.
The film begins with Hans reading aloud detective notes on the investigation of the disappearance of a woman, who was his and his siblings nanny, and death of their father. Hans summons his siblings who are now adults, to help him piece together what happened that day. All they remember is that Mary had rescued them from the fire before fleeing the scene.
Hans presents a notebook to his siblings and asks them why they hadn't seen it before. Hermann becomes angry and accuses Hans of creating the notebook himself, suspecting him of setting their home on fire twelve years before. Jonas appears, but quickly becomes anxious and has a panic attack. Hans and Anna attempt to calm him. Hans reads another journal and discovers that he and his siblings were subjected to torture experiments by their father and nanny, who were researchers who were studying unconscious manipulation. All the dates in the journal are noted to be Wednesday. It is written that the children were experimented on during those days. Jonas questions if he can remember a Wednesday, but cannot. The journal ends were it is written that the doctor had ended his experiments and his project was canceled. Anna and Hermann find themselves alone and Anna asks her brother why they cannot remember each other. Hermann tells Anna that he does not know the answer, but promises to protect her now.
Hermann sees Mary and tells the others. Hans finds a newspaper article and reads it to him explaining that Mary had died a few years previously by suicide. He reads on that Mary confessed to experimenting on children, and had been studying unconscious trauma. It is revealed then that the siblings are not true siblings but were adopted by Mary and the doctor, who the called father, with the intention of experimenting on them. Mary's apparition appears to Hermann again and tells him to stop the investigation. Jonas then becomes verbal and says that his hallucinations were real, explaining that he saw Mary.
Anna realizes that she cannot remember Wednesdays and it was a Wednesday, twelve years previously, was the day a fire destroyed their home and the doctor was killed. The doctor had hypnotized the children, then took them into a room where he tied the boys to chairs and forced them to watch him rape Anna. Hans wakes up from the hypnosis and breaks from the ties. This causes the doctor to stop what he is doing and flee the room. Hans calls the doctor back and pretends to be hypnotized. The doctor returns but is stabbed to death by Jonas. As the doctor dies, Jonas realizes what he has done and panics. Mary finds the children and the doctor's body. She tells the children they must hide the body. Mary hypnotizes the children erasing their memories, then forcing each to light a match and then set the room and then themselves on fire. As they burn, Mary begins to scream for help.
It can be assumed that Mary rescued the children from the fire once others arrived at the scene, but they did not survive. The children, having their memories erased, led them to believe they survived and therefore imagined they saw each other age as well.
The children awake in present day, as children again, and see Mary who asks them if they would want their memories erased before they go into the afterlife. All four come to the conclusion that they would rather keep their memories, and Mary leads them to the next life.
