Plot summary
After being silent for three days, when the Machine generates numbers of six missing people, Reese, Finch, and Detective Carter realize that they are hunting a serial killer who assumes the identity of his victims. Reese encounters FBI agent Alan Fahey ( Luke Macfarlane ) at Owen Island during his search for the same killer. Due to a severe storm, residents of the island take shelter in the police station. Finch arrives at the island and assists Fahey interrogate the people in the station. Carter, having researched the six victims, goes to help Finch and Reese.
Meanwhile, Finch and Reese discover that the killer is actually masquerading as Agent Fahey, whom he had killed before Reese arrived on the island. The killer captures Finch before Carter arrives and saves him before Beecher shoots the killer dead. Finch and Reese later ponder why the Machine was silent for three days, with Finch suspecting that the virus Kara Stanton uploaded to the Department of Defense has infected the Machine and slowed its abilities. He tells Reese that he believes this is the beginning of a coming storm.
Credits
Adapted from Wikipedia contributors, Person of Interest season 2. HTML formatting and reference markers removed.