Plot summary
Samaritan begins a series of power outages throughout the country. Having been sent by the Machine, Harper releases Fusco, but is caught by Dominic. The Machine allows Root and Reese access to its God Mode (from "Zero Day" and " God Mode "). Fusco and the NYPD arrest Dominic and Elias. Control believes "the Correction" is Greer's plan for a terrorist attack on the Supreme Court, but it's actually a list, created by Samaritan, of people who need to be eliminated for the betterment of society, including Control. Dominic and Agent Grice are killed by Samaritan snipers.
Elias is also shot. Root and Finch infiltrate Caleb Phipps' (from "2πR" and "Blunt") company to steal his compression algorithm and some high-capacity RAM chips, but Caleb willingly gives them to Finch. Reese regroups with Finch and Root at an electrical substation. They discover that the Machine spread itself over the power grid in boxes attached to electrical poles, and that Samaritan has been causing the power surges to destroy the boxes. Finch and Root starts downloading The Machine's core code to a briefcase contained with the compression algorithm and RAM chips. The team walk out with the briefcase to face more Samaritan operatives.
Credits
Adapted from Wikipedia contributors, Person of Interest season 4. HTML formatting and reference markers removed.