The Machine identifies Darren, a teenager whose brother was just murdered, as the next POI. Meanwhile, Finch is growing concerned that the son of his former business partner is dangerously close to finding out about the Machine.

Carter tries to help Reese by engaging in mental warfare with the FBI; Reese has encounters with old and new enemies; Detective Fusco must protect supermodel Karolina Kurkova, the latest person of interest.

Finch and Reese meet their match: a tech billionaire whose curiosity and endless resources could expose their identities and ruin their efforts to save his life.

When a person of interest is poisoned, Finch and Reese only have 24 hours to identify the toxin and find the person responsible; Detective Fusco's past catches up to him.

The Machine, now completely self-governed with its whereabouts unknown, resumes giving Finch its "irrelevant" numbers for people in danger, which include a U.S. naval officer in town for Fleet Week. However, with so many sailors flooding the streets of New York City, finding the officer in time presents an even bigger challenge for Reese and Shaw.

As the POI team seeks justice for Carter’s murder, Finch realizes one of his team members may go one step too far in order to end the war with HR. Also, The Machine gives out the number for NYPD Officer Patrick Simmons, one of the crime organization’s key players.

When an unknown entity prevents The Machine from seeing the full picture of an impending catastrophic event, it sends the team five separate numbers to help them piece together the bigger picture. Meanwhile, Root’s team of hackers arrives in New York.

The team takes desperate action in its race to prevent the malevolent AI program Samaritan from coming online and making them its first targets. Meanwhile, the months-long battle with the anti-surveillance terrorist group Vigilance comes to a shocking conclusion.

Despite not wanting to help with the new numbers, Finch's interest is piqued when the newest person of interest turns out to be a brilliant college student involved with a mysterious scavenger hunt.

Reese's cover job as a detective at the NYPD becomes complicated when the young brother and sister he's protecting become targets of a gang investigation.

Samaritan launches a cyber-attack on the stock exchange, forcing the team to risk their lives in a desperate mission to stop a global economic catastrophe.

Reese and Finch try to protect a psychologist whose unorthodox methods for helping his patients find closure could cost him dearly. Meanwhile, flashbacks reveal Finch’s fragile state in the days following the bombing that killed his best friend, Nathan Ingram.

Finch and Root race to save The Machine, which has been located by the rival AI, Samaritan. Also, Reese is caught in the middle of the final showdown between rival crime bosses Elias and Dominic.

Reese and Finch attempt to rescue the Machine’s source code before it deteriorates beyond repair. Also, Root fights for her life against an onslaught of Samaritan’s agents and Fusco is faced with hard questions following the deaths of Dominic and Elias.

The Machine experiences a glitch during rebooting, supplying Reese and Fusco with the numbers of dozens of people not actually involved in crimes, while also locking Finch and Root out after identifying them as threats based on past violent behavior.

Shaw escapes her captors, but the team is unsure of her mental state when she begins to act paranoid and reckless.

Finch, Reese, Fusco and Shaw embark on one last mission to prevent Samaritan from destroying The Machine and cementing its hold over mankind.