Plot summary
Reese and Fusco follow a bounty hunter named Frankie Wells ( Katheryn Winnick ) whose number has come up. She is trying to track down the man ( Ato Essandoh ) that killed her brother. Harper Rose ("Blunt") interjects herself into the cat-and-mouse case and manages to negotiate a resolution to a gunfight standoff between Reese and several other parties. Later, Harper tells Reese that Thornhill (The Machine) has been sending her texts. Finch resumes meeting with Elizabeth Bridges, whose number also came up. She is nearly ready to turn over a software package that contains the Trojan Horse which Finch had installed previously.
He intends to activate it via a special device. Root, fearing that this will result in Finch being exposed and killed by Samaritan agents, foils the plan, at the cost of Finch and Elizabeth's growing mutual attraction. A doubly devastated Finch tells her to leave the team for a while. Iris confesses to Reese that she has fallen for him.
Credits
Adapted from Wikipedia contributors, Person of Interest season 4. HTML formatting and reference markers removed.