Plot summary
Flashbacks illuminate Finch's dealing with survivor's guilt, Reese's time doing wetwork, Shaw's former life as a technically excellent surgeon but completely indifferent to the people she helped, and Fusco's recounting of exacting vigilante justice to a crook that slipped through the system (the devil's share). Reese starts sliding into his old, dark ways to get Simmons while also sliding towards death. Finch, Fusco, and Shaw go to an HR attorney to know Quinn's whereabouts to question him for Simmons' plan, but the Russians have killed him, shortly after Reese got the information.
The team turns to Root in desperation. Reese gets Simmons' location and is just about to kill Quinn when Finch reminds him that killing Quinn now would destroy Carter's legacy of bringing him down legally, and he collapses. Fusco finds the note that Reese dropped, and goes after Simmons. After a brutal fistfight, Fusco emotionally refuses to kill Simmons and takes him into custody, citing Carter's influence for turning his life around. Root, despite having opportunity to flee, returns to her cell, and Finch thanks her for helping him in saving Reese. Finally, Elias watches as Marconi murders Simmons in his hospital bed in retaliation for Carter.
Credits
Adapted from Wikipedia contributors, Person of Interest season 3. HTML formatting and reference markers removed.