The Box

In December 1976, a financially strapped couple, Norma (Cameron Diaz) and Arthur Lewis (James Marsden) find a package on their doorstep. Inside is a locked wooden box, with a transparent dome top and large red button visible underneath. An accompanying note reads: "Mr. Steward will call upon you at 5:00 pm". They leave it in the kitchen.
At 5:00 pm, Mr. Steward (Frank Langella), a mysterious man with the left side of his face burned off, arrives to deliver a key to the box. He tells Norma that, if the button is pushed, he will give her a tax free payment of $1 million in cash. However, someone she does not know will die. Arthur, a NASA engineer, disassembles the box to find only a button and nothing under it.
Later, Norma and Arthur have ethical and moral arguments about pushing the button, wondering whether a young and innocent person, or a person on death row will die. Norma impulsively decides to push the button, and does it quickly before her husband can stop her. Simultaneously, miles away, a man kills his wife and then flees, leaving their daughter locked in the bathroom. Police are perplexed as to why Jeffrey Carnes (Ryan Woodle), a NASA employee like Arthur, shot his wife to death, because they had a happy relationship.
At Norma's sister's wedding rehearsal, Arthur wins a chance to select a gift from presents provided by the dinner guests. A plain brown box exactly like his and Norma's is among them. Arthur opens it to find a photo of Steward before the disfigurement. Arthur asks Norma's father, a police officer, to run the license plate number of Steward's car. Shortly after, Norma is asked to take a phone call at the wedding rehearsal. The call is from Mr. Steward who asks why her husband is having his car license plate run by the police department. Norma asks Mr. Steward how he knew this, and he warns her that he has employees everywhere.
Later on, Arthur drives the babysitter (Dana) home. She tells him she is living in a motel because her family is moving, but their new house is not ready to move into yet. As he is driving, she begins to ramble and tells Arthur to "look into the light" and asks if "somebody is pushing his buttons." Her nose begins to bleed and she passes out just as he is approaching the motel. Arthur pulls into the motel parking lot and sees her ID, which states that her name is Sarah Mathews, not Dana. She suddenly wakes and rushes into the motel. In her room, she has surveillance photographs of Arthur and his family all over the walls. It is obvious she is not who she says she is. Once back home, Arthur asks Norma how she met the baby-sitter; she said on a tour of the Kennedy Center in Washington, D.C.
Later, while in the supermarket, Norma is approached by a woman who tells her to look up a certain call number in the library and not to trust anyone, not even her husband. The woman, who was the inquisitive journalist at a conference Arthur was present at earlier on, also passes out with a nose-bleed. Norma's father discovers Steward's car is registered to the NSA and allows Arthur to visit the Carnes home crime scene. Arthur finds pictures of Steward and a Human Resource Exploitation Manual along with a library call number.
Norma and Arthur separately visit the library. Arthur approaches Steward's wife (Deborah Rush), who leads him into a room with three upright cuboids of water. Two will lead him to eternal damnation, while the other leads to salvation. Arthur enters one and he vanishes, while Steward's wife leaves the library alone. Norma is led by two women to Steward and has a discussion about how he had gotten his facial disfigurement as a consequence of being struck by lightning while working at NASA. He causes her nose to bleed and she passes out. She finds herself back at home upon her bed. Above her, Arthur emerges within a rectangular cube of water and he is flushed out and falls on her. They both leave in shock and prepare for the wedding reception which is that evening.
Back at the NSA, the NSA chief and Arthur's boss at NASA discuss Steward. The chief tells Arthur's boss Steward is "something else." When Steward was struck by lightning, he died, but at the morgue, a nurse heard Steward laughing. His body supernaturally regenerated; he was transferred. The NSA chief and Steward discuss the "box and button."
At the wedding reception of Norma's sister, Arthur and Norma's son Walter (Sam Oz Stone) is kidnapped. Arthur is forced to leave at gunpoint, by Jeffrey Carnes, who reveals that he had been forced to choose between his wife or daughter, and also informs him that they have to save Walter or Norma will die, and that he will kill her if they do not save him. Carnes is forced to stop his car by a man dressed in a Santa costume standing in the road. The car is then hit by a truck, knocking Arthur and Jeffrey unconscious.
Meanwhile, NSA employees round up large groups of people, including Arthur and Walter. Steward oversees the process. Steward's boxes are an experiment to judge whether a majority of individual members of the human race will put other lives before any personal gain. If a majority push the button, the human race will be exterminated. All the test subjects are couples under 40 years of age with one child.
Steward offers Arthur and Norma a final choice. Walter is now deaf and blind. They can either live on with $1 million and a disabled son, or Arthur can shoot Norma through the heart, at which point Walter's sight and hearing will be restored and the $1 million in a trust fund for him. Norma begs Arthur to shoot her. Elsewhere, a woman pushes the button on her box and Arthur shoots Norma, killing her. As Arthur is taken away by police, Steward leaves the other couple's house with the box. Walter is shown through an upstairs window in the home with his grandfather (Holmes Osborne). The final scene shows Steward standing in the snow by his car, parked in a street, with the box.

Question: Who vanishes during a trip to the library?
Answer: Arthur