In Boston, Massachusetts, an Observer is timing an event and making notes in his journal. As he watches people walking by, a veteran selling American flag pins approaches and asks him about the binoculars he's using. The Observer says they're from somewhere far away. The man puts a pin on his lapel and leaves, and the Observer notices a young girl, Christine Hollis, walking by. He places the binoculars in a briefcase containing a teddy bear and approaches the girl, leaving his journal behind. The Observer grabs the girl and starts pulling her away. When a man intervenes, the Observer draws a gun and fires, blasting the man several dozen feet back. He then steals a car, injecting the girl with some kind of sedative. A security guard arrives and fires, seemingly missing. The Observer gets in the car and triggers the ignition with a touch, and then drives away.
Olivia is sleeping on her couch when her niece Ella comes in and reminds her that they're going to the amusement park. Olivia insists she's not going on any roller coasters because she's scared of them. She gets a call and then tells Ella they'll have to delay until later, and her niece says that she knows her aunt has an important job.
Olivia goes to Peter and Walter's house and tells Peter that the Observer was apparently spotted, and they're waiting for the security footage. Walter is busy in the kitchen making a milkshake because his favorite soda shop closed down. Olivia finally pulls Walter away and they go to the lab. She asks him what he knows of the Observer. Walter insists there's nothing more he can tell her other than the fact that they were drowning in a car crash when Peter was a boy, and the Observer saved them. They receive the downloaded footage from the security cameras and Olivia realizes it's not the same Observer they know of. Meanwhile, Broyles has recovered the journal and is sending it to them. They go over the footage in slow motion and see him catch the security guard's bullet.
The pseudo-Observer takes Christine to a motel in Lowell, Massachusetts and ties her to a bed. When she tries to plead with him, he recites every word she says as she says it before finally gagging her. He the dons his hat and leaves.
Broyles identifies Christine and passes on what information they have to Olivia. She has no parents and no significant record, and Olivia admits she has no idea how the facts tie together. Broyles believes that the key is Christine, and figuring out why the Observer made an exception to take her.
At the lab, Peter finds a spot of blood in the journal. He asks Walter if the Observer said why he saved them, and Walter says he didn't. Peter believes that they're close. Astrid tries to decipher the writing, which contains 1,246 distinct non-repetitive characters. As Olivia arrives, Walter notes that the blood has an orange tint, suggesting hemophilia. As Peter puts out an alert to hospitals to get a list of hemophiliacs, Astrid discovers that someone else has been researching the symbols.
Olivia and Peter meet with Brandon, the scientist at Massive Dynamic who has been deciphering the symbols. One symbols is a cuneiform found on an ancient Iraqi tablet. Another symbol dates back to 900 B.C. However, Brandon has no idea what they mean. However, he reveals that he found something else. He shows them that he's found an engraving of the Boston Massacre that shows the Observer in the background. Brandon has found other pictures and drawings of the Observer from France 1793 and Sarajevo 1914. He explains that the Observers may be able to view time and go to significant technological and historical events. Brandon has charted 26 sightings in the last three months, but only a dozen in the preceding 5,000 years. He wonders what is about to happen.
The Observer and two other Observers meet at a restaurant and enjoy a meal with hot sauce. They realize they have a situation with the abductor, August, and review the security footage. One of the Observers notes that Christine is supposed to be on Tropos Air, Flight 821. They don't know why Christine was abducted, and they realize August has created an anomaly. They decide to contact Donald.
Donald Long gets a signal from the Observers. He goes to his car and takes out a case, and then receives a fax with a picture of Christine. Donald takes out a gun and attaches a silencer to it, and then considers Christine's picture.
Olivia and Peter go to Alliston, Massachusetts, and talk with Christine's friend Danielle. Danielle explains that Christine was supposed to take a flight to Italy that day and Olivia asks for a copy of the itinerary. Peter finds a photo of a young Christine with her parents, and Danielle explains that Christine's parents died during the big earthquake in San Francisco in 1989. As she goes to get the itinerary, Peter points out that the Observer can be seen in the background of the photo.
Christine finally manages to pull herself free and falls over. August arrives with food and places her back in her chair, and then ungags her so she can eat. When he sees the bruises on her arm, he appears sympathetic and then offers to show her what he wants. He turns on the TV and tells her to wait.
As Olivia and Peter drive back, Olivia calls the neighbors who are watching Ella. She's out getting ice cream. Peter wonders why she's upset and Olivia explains that she isn't happy that their special day was interrupted. She talks about the first time her mother took her to a movie and what a thrilling experience it was. They hear a broadcast on the radio about Christine's flight to Italy crashing and everyone on board dying.
The news broadcast plays on the motel TV and August explains that she was going to die and he saved her. However, he warns that she's not safe yet and there's something he needs to do. August ties her up again and gags her for what he claims is his own protection.
Peter and Olivia arrive at the lab and explain to Walter what happened. They wonder what is special about Christine. Astrid gets the results of the blood sample and they realize it's capsaicin: chili pepper juice. They are particularly hot and Olivia realizes that they can track anybody who imports them.
August goes to the Indian restaurant and finds the other three Observers waiting for him. They ask for an explanation and ask who Christine is. August explains he has observed her entire life and she is unique, and that they have interfered before. The Observer notes they have only done so to correct a mistake of their own making. August says that he can see that Christine is important but the others believe his perception is in error. August concedes the possibility and they inform him that his oversight will be overlooked but they have already seen to correcting the mistake.
Olivia and Peter go over Christine's records but can't find anything significant. Astrid has an address on one private citizen who ordered the chili peppers. As Peter and Olivia leave, Walter has Astrid tastes his new attempt at recreating the milkshake. He asks her to go to the market, but once she's gone, Walter grabs his coat and leaves.
Donald breaks into August's apartment and finds photos of Christine throughout her life taped to the walls.
Walters goes to the Indian restaurant where August is waiting for him. He left Walter a message consisting of a nitrogen molecule to catch his attention. Walter asks him not to take his son, and explains he had an arrangement with the Observer. August, surprised, says that he contacted Walter because he needs his help. Walter wants to call Peter and Olivia, but August notes that they're occupied.
Olivia and Peter arrive at the apartment, unaware that Donald is inside and searching the place. He finds a phone book with a page slightly warped to indicate a motel. Peter and Olivia break in and split up to search. Donald gets behind Peter and tells him to get to the ground. Peter attacks him but Donald escapes out the front and disappears before Olivia can catch him.
August explains to Walter that he has interfered in the normal course of events, and they won't stop until Christine is dead. He has no idea how prevent her death, but notes that Walter has solved a similar problem before by seeing past the limitations of the situation. Walter admits that he just missed his son. He asks what is special about Christine and August admits that he can only see it, not describe it, but the other Observers don't see it. Walter suggests that August do what is necessary prove she is important, and be ready to accept the consequences.
Olivia and Peter go over August's apartment and find a newspaper dating back to 1884.
August returns to the motel and asks her if she trusts him. Christine says that she does and he says he must do exactly what he says.
A FBI forensics team goes over the apartment and looks at the other old newspaper articles pinned to the wall. Peter wonders what the Observers are looking for. Olivia gets a call informing her that August has been spotted in Lowell.
Donald breaks into the motel room in Lowell and doesn't initially find anyone. He spots a closet door and approaches it, and August shoots him with the pulsar gun and knocks him back. He then goes outside and Donald demands to know where Christine is. Olivia and Peter pull up and August tells Donald "Goodbye" and then lets himself be shot. Donald flees and Peter run to August. August grabs Peter's hand and gives him his gun. Olivia goes after Donald but he manages to get behind her. As he prepares to kill her, Peter shoots him with August's gun and the assassin falls off the roof to his death. They go back to the parking lot and discover that August has disappeared. Olivia goes back to the motel room and discovers Christine hiding behind the bed. She asks about August and Olivia takes her home.
The Observer drives away with August and asks why August saved her. August explains that he saw Christine as a child. She was crying after her parents died, but he realized she was brave. She crosses his mind and never left it, and he wonders if he loves her. August asks if she'll be safe and the Observer says that she is now, that August made her important by making her responsible for the death of an Observer. August dies of his wound.
Back at her apartment, Christine wonders what it all meant. Walter comes in and tells her that he has something from August he was told to give her. He gives Olivia the teddy bear and she remembers it was the prize her father won for her. She was holding it during the earthquake. Walter tells her that he thinks she'll be safe now. Outside, Peter wonders when Walter saw the Observer. Walter assures him that he'll get his answer, and suggests they go for a long drive together to get a milkshake.
Broyles confirms that Donald was connected to a series of assassinations dating back ten years. There was nothing on his car to indicate who hired him, and the techs can't get the gun to fire again. Finally, Broyles tells Olivia that someone tipped them off from another phone at the motel. They figure that August called them when he couldn't protect Christine herself. Olivia asks for a day off. Later, she goes to the amusement park with Ella… and rides the roller coaster. They're unaware that the Observer is watching them from the ground. Another Observer comes over and notes that things will soon become very hard for Olivia.