Inside a hospital, a priest delivers the last rites to an unidentified patient. Meanwhile, a man we will come to know as Samiel makes his way through the hallway of a moving train. He steals a set of keys from a conductor's station, then makes his way to a compartment holding four passengers, including a little girl Jordan's age. Samiel uses a key to lock the compartment door. Moments later, the trains wrenches violently and plunges into a river. Back at the hospital, the priest continues his prayer, identifying the patient as Jordan Black.
In flashback, two days earlier: As Frank stops the red Cherokee in front of the elementary school, Jordan complains of not feeling well. Frank promises he will pick her up at school if she still feels under the weather at lunch time. Meanwhile, inside a park, a mother videotapes the strange sight of a middle-aged woman flailing her arms and gasping for breath. As the stricken woman collapses, water streams from her mouth.
Emma and Frank investigate the woman's death. Frank experiences a vision, one that prompts him to conclude that the woman drowned. However, Emma explains that the victim died on dry land. A coroner finds a large amount of water in her lungs. Moments later, Frank experiences another vision. He sees more water and still more bodies. He also notices an indent on the victim's wrist, indicating she wore a watch.
Emma tells Frank that a woman named Lisa Maher also died as a result of the mysterious fluid. It turns out that Maher once suffered from meningoencephalitis, a bacterial infection of the brain which usually proves fatal to adults. Jordan also suffered from the ailment years earlier. Frank discovers that Gertrude Epstein, the woman from the park, miraculously survived a terrible car crash three years earlier. The common link between Epstein and Maher is that both cheated death. Later, Samiel enters a tenement apartment where he approaches a sleeping thirty-five-year-old man. Samiel places his hand over the man's mouth, causing water to stream out.
Frank and Emma investigate the man's death. It turns out that Samiel dialed 911 and alerted authorities of the victim's demise. Frank believes it was an act of compassion. A search of the dead man's apartment turns up a postcard for meetings at Remain in Light, a near death experience group. Later, Frank picks Jordan up from school when she continues feeling sick. As he walks towards the Cherokee with his daughter, Frank notices Samiel standing under some trees, watching from the shadows. Suddenly, Jordan collapses. Frank rushes her to the hospital, where she is placed in a tub of ice to lower her body temperature. Eventually, Jordan's condition stabilizes. A doctor tells Frank that Jordan exhibits symptoms of meningitis, but lab tests have ruled out the disease. Frank insists the illness is not a figment of Jordan's imagination. Moments later, he notices Samiel standing under a large tree two floors below. Frank races outside the hospital, but by the time he reaches the tree, Samiel is gone. Frank finds a woman's watch hanging on one of the tree branches.
With the assistance of a computer sketch artist, Frank creates a drawing of Samiel's likeness. Frank tells Emma that the stranger has been stalking Jordan. He also links Jordan's previous brush with death (when she was diagnosed with meningitis years earlier) with the other three victims. He believes that all four people, including his daughter, have been living on borrowed time. And now, for reasons unknown, Samiel is coming after Jordan. Emma assures him that Jordan's sickness has nothing to do with the case.
Emma discovers Samiel attending a Remain in Light meeting. She escorts him to Quantico for questioning. Frank suddenly launches himself at Samiel. He warns him to stay away from his daughter and threatens his life. Emma and several agents pull Frank off Samiel. Shortly thereafter, he learns that tests have concluded that Samiel's voice does not match the 911 call. Frank studies the videotape taken at the park. He discovers Samiel's reflection on a window near the collapsed woman. Frank plays the tape for Emma. As the images advance, frame by frame, it becomes clear that Samiel's reflection vanishes in one frame. Emma insists the man could not just disappear into thin air. Moments later, Jordan steps from the shadows, gasping for air. Water begins trickling from her mouth.
Doctors stabilize Jordan's condition, but are confused by her symptoms. A short time later, Samiel approaches Frank at the hospital. He tells Frank that Jordan must die in order for others to live, just as Catherine died for Jordan's sake. Frank rushes to his daughter's side when alarm monitors begin to blare. Doctors wheel in a crash cart and attempt to save her life. Frank begs God not to take his little girl away.
As Jordan begins to drown in the mysterious fluid, Samiel locks the compartment door on the train (as seen in the opening teaser). As before, the train lurches off the tracks and plunges into the river below. As water pours into the train, Samiel becomes trapped in a corridor. As the last bits of oxygen escape from his lungs, Jordan's heart begins beating once more. A short time later, paramedics rush the first of the four train wreck survivors into the emergency room. A paramedic points to a sheet-covered body nearby. He states that the victim did not share their luck. Emma pulls back the sheet and sees Samiel's body, a peaceful smile upon his face. Later, Jordan tells Frank she spoke to Catherine, and that her mother said to convey a message: she made the right choice.