Tracy Beaumont, a young girl, pulls away from another man and walks away. When a policeman, Sgt. Robert Lorizano, stops her and asks if she’s okay, everyone suddenly goes berserk and attacks each other. Tracy tries to crawl out while the police officer struggles with a woman who grabs his gun. After a brief fight she shoots him.
At the office, Gary tries to find the source of the humming noise that annoys him. He finally tells Bill that it’s coming from the microwave station across the street, and the company won’t keep it shut down. When Bill refuses to give him his gun to shoot it, Gary asks Nina to push someone while examining her shoes. Meanwhile, Cameron tries to negotiate with his wife for more time with his son. Rosen visits Rachel and discovers that she’s using aromas that relieve stress. He figures that that her meeting with the man her parents have chosen for her didn’t go well, and suggest that she be more assertive just as they discussed. Rosen goes to see a frustrated Cameron, who is losing control of his ability. He assures Cameron that Tyler will be his son no matter what. Irritated, Cameron throws a baseball and breaks a window, but Rosen assures him that he’s made strides.
Don calls Rosen and his Alphas to the subway station to investigate the riot. Nina talks to an officer who insists that Lorizano didn’t start the riot. She pushes him into leaving and tells Rosen that she doesn’t like it when people ask questions. Bill arrives late and complains that they didn’t wait for him. Gary scans the EM traffic but doesn’t pick up anything useful. Bill notices that Cameron has gone out for a cup of coffee and the police won’t let him back in. He gets the police to let Cameron in and complains that he left a crime scene.
Don shows up and tells Rosen that there have been four unexplained riots in the last three months on the East Coast. Rosen will only admit that Alpha involvement is a possibility, and Ron insists that they need to find the Alpha before the police or the press locate her. As Don goes, Rosen has him use his credentials to acquire the security footage. Meanwhile, Rachel goes through the subway car and uses her enhanced smell to locate a stuffed monkey covered in a particular odor.
Back at the office, Bill confirms that the other riots followed the same pattern. Rachel explains that the Alpha responsible used pheromones to influence the entire crowd to feel a single emotion when she was threatened. Cameron wonders why they are involved when Bill is the only law enforcement official among them. Rosen insists that as Alphas they are the only people who can handle another Alpha. Gary receives the streaming footage from Don and complains about the hum again.
In his office, Cameron bounces pencils into the ceiling as Nina comes to visit him. She insists that what Rosen said is important and that the doctor was able to help her. Nina insists that Cameron’s hyperkinesis comes in handy and says that what matters is what he thinks. Meanwhile, Rachel spots the stuffed monkey on the security footage, hanging off of Tracy’s backpack. Bill soon identifies her and learns she was taken to a hospital, treated for cuts and bruises, and released before the police could interview her. Cameron reluctantly gets involved, noting that “Tracy” may be an alias. Bill goes to check out Tracy’s background and tells the others to stand by. Gary has to be home by 9:30 and Rosen sends him there to check the security cameras.
Rachel goes home and her mother nags her about meeting a man despite her “condition.”
Gary locates Tracy via the security cameras and calls Rosen. The others go to the address and Rosen gives Don an update. Rachel tries to track the pheromones but loses them in the crowd. Bill takes Cameron and searches one direction while Rosen, Nina, and Rachel go in another. They call Gary, who directs them toward Tracy’s location. Rachel spots Tracy and the girl runs into a youth hostel. A fight breaks out and spreads onto the street. Tammy runs out across the street and Bill goes after her. The boy from the subway runs out of the hostel and calls to Tracy, and Rachel recognizes him from the subway. As the boy runs past Cameron, he trips him. As the police arrive, the boy denies knowing anything at first. He finally says that Tracy is his sister and he’s immune to her ability. Meanwhile, Bill loses Tracy in traffic when she takes a cab.
Cameron picks up Gary and brings him to the office, while Rosen updates Don on the situation. The doctor begins an interview, recording what the boy says. He says that his name is Matthew Hurley and Bill runs a background check. When Rosen points out that his sister’s name is Tracy Beaumont, Matt explains that Beaumont was their mother’s maiden name. Their father beat his wife to death three years ago, apparently under Tracy’s influence. Matt claims that his sister’s real name is Alice and she changed it to avoid being connected to the events in their hometown, Arden, OH. He insists that he’s the only one who can keep Tracy in control.
Gary tries to check the Arden homepage but gives up when the humming becomes too great for him. Meanwhile, Rosen explains that Tracy has a medical condition and he wants to help. He believes that Matt’s brain produces high level of serotonin to counter her pheromones, due to long-term low-level exposures. Matt considers the doctor’s offer of help.
As Cameron and Nina discuss whether she should use her ability on Matt, Don arrives with two of his agents. Rosen meets him in the hallway and says that he can win Matt’s cooperation if Don will get out of the way. When the DoD liaison says they need to get Tracy to Binghamton, Matt overhears them and wonders what don has planned. Gary comes in and tells them that Tracy is at the bus station.
Don argues with Matt while Rachel calls her mother. Meanwhile, Bill finds a photo of Alice Hurley and confirms that she looks nothing like Tracy. Don and his men restrain Matt and he releases pheromones. Everyone in the room except Bill goes berserk. Rachel screams at her mother over the phone while the Alphas attack Don and his agents. When Bill tries to stop his friends, they attack him as well. Matt runs for the elevator and Don chases him, but one of his agents beats him to death with a chair.
Once the effects of the pheromones dissipate, the team finds the agent crying over Don’s corpse. As the containment teams arrive, Rosen explains to Bill that the pheromones didn’t work on him because he controls his fight-and-flight ability. The others try to deal with being controlled against their will and seeing Don die. Rachel leaves for home and Rosen asks Nina to take Gary home as well. The doctor then gives Cameron serotonin to resist the pheromones.
Matt finds Tracy at the bus station and says that he’ll go with her. She tells him to calm down and explains that she ran away to get away from him. Bill and Cameron arrive and Matt threatens to start another riot. When they close in, Matt releases a wave of pheromones and runs off. The passengers go berserk, overwhelming Tracy. Bill runs after Matt while Cameron uses a fire extinguisher to hold off the crowd long enough to pick up Tracy and carry her cross the shoulders of the crowd to the safety of a balcony.
Bill corners Matt on a bus. The teenager unleashes another wave of pheromones and tries to get out the back door, but Bill knocks him unconscious.
Later, Nathan Clay picks up Matt and takes him to Binghamton. As they talk, Rosen hears people screaming in the background. Nathan tells him not to worry about it and comments that he’s only human. Rosen insists that his people are human and so is Matt, and Nathan needs to treat them as such. As they talk, Rosen takes the tape of the interview and puts it in a case with other tapes, all labeled “Binghamton.”
Rachel visits Nina and they both try to cope with Don’s death. She tells Nina that she was on the phone with her mother and said she was going to move out. Rachel plans to live with her cousin but Nina invites her to stay at her three-bedroom apartment. She suggests that they can both use the company.
Rosen meets with everyone to discuss everything that happened to them. Gary talks about Don’s brains being bashed in and Bill takes offense. Rosen insists they all have valid ways to deal with their grief. He then says that Agent Sullivan will probably replace Don and that he died because he didn’t give them his trust. Rosen admits that things will be messy but there is nobody else who can do what they do. Gary starts to talk about death but complains about the humming and how no one has helped him.
A few minutes later, Cameron invites Gary to walk with him to the roof. As Nina watches, Gary points out the antenna that is bugging him. Cameron throws a baseball and knocks out the antenna. As they go inside, Gary says that he isn’t worried about the future and Cameron admits that he isn’t as well.