A mystery man named Finch contacts an ex-CIA agent, John Reese, and offers him the chance to save people. Finch can identify someone involved in a future violent crime, but is unable to confirm if they are the victim, the perpetrator, or a witness. Reese's first case: determine what danger a young woman district attorney faces and stop it.
The Machine gives the Social Security number of a girl that has been dead for two years. Reese and Finch try to track down an apparent ghost while Finch remembers his partner's objections when he first created the Machine.
Songs: Handsome Boy Modeling School -- The Truth
Reese and Finch try to help an ex-Marine who is working with a gang of other ex-soldiers who rob banks to cover their debts. Meanwhile, Carter comes to the realization that Reese isn't the cold-blooded killer she initially believed.
Dr. Megan Tillman, a workaholic ER physician, comes up on the Machine. While Reese and Finch watch her, Fusco has to deal with a drug cartel that wants their drug money back.
When a judge's son is kidnapped, Reese and Finch try to help him. However, he isn't interested in putting his son in further danger by accepting their help.
Songs: The XX -- Intro
Reese needs to get close to a secretive woman of uncertain occupation when her number comes up. Meanwhile, Carter investigates a murder tied to the evidence theft.
Reese and Finch hurry to save a schoolteacher who witnessed a mob hit. Meanwhile, Carter and Fusco pursue the mysterious Carl Elias, who is implicated in the murder of the man the schoolteacher saw die.
A Cold War assassin goes after the members of his former team, and Reese and Finch try to stop him. Meanwhile, Fusco attempts to convince Carter that her shooter can do some good.
The Machine gives Reese and Finch Carter's number, and they are forced to deal with a number of suspects when they realize that crimelord Carl Elias has hired someone connected to her to kill her.
Songs: The Radio Dept. -- It's Personal
The Machine gives Reese and Finch four new numbers, and they soon discover that one of the Persons of Interest is already dead. Meanwhile, IA investigates Carter for her involvement with the mystery man, and the CIA tells her that they want Reese back.
Songs: Unkle -- When Things Explode
A wounded Reese recovers from his injuries, and Finch sets him up at an apartment building where the Machine has given them the super's number. Meanwhile, the CIA follows Carter in the hopes that they can find Reese through her.
Reese and Finch get the number of a young woman who is suing the state on behalf of convicts, and discover that someone wants her dead. Meanwhile, Finch visits with the son of an old friend, and Carter helps Reese for the first time.
Reese and Finch take on the case of a out-of-work construction foreman who is soon framed for the murder of a congressman. Finch soon discovers that he's up against a mysterious hacker who is his technological equal, and turns to former Person of Interest Zoe Morgan for help.
While Reese, Carter, and Fusco protect a young teenager out for revenge on the gangers who killed his brother, Finch worries that his dead partner's son Will will track down the woman who knows about the creation of the Machine.
Reese goes undercover as part of a smuggling to track down the Machine's new Person of Interest, but soon realizes that he's dealing with an undercover cop. Meanwhile Fusco is forced to approach the crooked cops, his former associates, to help out Reese.
Reese and Finch discover that their newest Number is a Wall Street prop trader who may be in involved in a multi-million dollar scam that will rob thousands of investors of their life savings.
Reese and Finch discover that their next number is a six-month-year old girl who needs protection when her mother is killed and the baby is left at a clinic. To save her, Reese must turn to Elias for information despite the risks. Meanwhile, Fusco and Carter are both forced to choose sides.
Reese and Finch must deal with a new Number who has very little electronic footprint. However, they soon discover that their "client" is actually two people with the same name, SSN, and bank accounts... and one of them is in great danger.
Songs: Polica -- Amongster
Reese and Finch receive Numbers on five Mafia Dons in New York City, and realize that Carl Elias is making his move. Meanwhile, HR leans on Fusco to produce Reese, and Elias leans on Carter to cooperate with him by abducting her son.
Songs: Unkle -- Burn My Shadow
Reese's newest number is an armored car hopper and Reese goes undercover as his guard to protect the man. Meanwhile, Snow warns Carter to avoid the FBI while Fusco becomes further entangled with HR.
Finch tries to keep Reese off of a case by giving him his birthday off, but Reese soon learns about it anyway and realizes it related to a personal incident in his life.
Songs: Danger Mouse & Sparklehorse -- Revenge
The new Number is a security analyst who has uncovered something that the government wants to remain a secret: the existence of the Machine. Meanwhile, Reese digs into Finch's past and discovers what he's been keeping hidden.
Reese and Finch set out to protect their newest Number, a psychologist who has been targeted for death by one of her clients. However, they soon discover their new case is anything but simple when HR, the FBI, and Alicia Corwin all come after them.
Root explains to the captive Finch what she plans to do for the Machine. Meanwhile, Reese tries to track down his partner but discovers that the Machine is less than cooperative.
Carter and Reese travel to Texas to unravel a 21-year-old missing child case and get a line on Root... the mysterious woman who has abducted Finch and Weeks, and plans to find the Machine no matter what it takes.
Reese returns to the field to protect an ambassador's daughter who is threatened by mysterious assailants. Meanwhile, Carter meets Agent Snow, who is also looking into Corwin's death.
Reese and Finch discover that the man they've been assigned is a mob enforcer ordered to kill the wife of a dead mobster. However, they soon discover that the enforcer is in love with the woman, and have to decide rather to protect him as well or let him die.
When an investigative reporter gets too close to the head of HR, her number comes up and Reese must get close to her without revealing that he is the mystery vigilante. Meanwhile, Fusco finds himself torn when Simmons tells him to help HR... or else.
Songs: DJ Shadow -- Building Steam with a Grain of Salt
The Machine's newest Number points to a hardware store owner living in the suburbs. When Reese goes undercover, he soon discovers that the man is hiding a dark secret from his past.
The Machine directs Finch and Reese first to Leon Tao, who has gotten in trouble again, and then to a doctor who is being forced to kill a patient to save her wife.
An unhappy couple hire hitmen to dispose of each other, and both of their Numbers come up. Meanwhile, love is in the air for Fusco and Carter, while Finch reminisces about his past with Grace.
-- One of These Mornings
A Cuban defector comes up as the next Number and Reese and Finch try to pinpoint who might be after him. Meanwhile, Carter tangles with the Secret Service while HR tries to make amends with Elias and sends Fusco to negotiate.
While the FBI close in on Reese, he fights to save a young couple who are out to take down a crooked loan officer who conned military veterans out of their money. Meanwhile, Carter gets a job offer and Fusco investigates her new boyfriend.
While the FBI try to confirm that Reese is the man they've been seeking, Finch and Fusco take on a new Number: a high school student with knowledge of computers.
At Donnelly's request, Carter interrogates the captive Reese in an attempt to confirm that he is the "man in the suit." Meanwhile, Reese tries to dodge an assassin sent into prison to kill him while Fusco protects a super-model whose Number is up.
Reese's former partner and lover, Kara Stanton, abducts him and forces him to participate in her plan to break into a DoD facility and steal a computer virus.
The team's new Number is a self-centered muli-million dollar web developer whose erratic behavior makes it impossible for Reese to follow him. Since he can't beat him, Reese joins him, but soon discovers that he and Finch have been compromised.
Songs: M.O.P. -- Ante Up
The team's new Number is a hotel maid and Reese and Finch infiltrate the hotel where she works. They soon discover that a Serbian hit squad is out to kill her. Meanwhile, Carter must pass a polygraph test to get a position with the FBI.
Reese and Finch try to help a CTU operative, Sam Shaw, who receives her targets' Social Security Numbers through the government. When she learns too much, the government wants her dead... and when Reese and Finch find her, Sam refuses their help.
Songs: The Kill -- Future Starts Slow
The Machine sends Finch and Reese six Numbers and they soon discover that they belong to six missing persons... and the sixth one disappeared on an island in the middle of a heavy storm. Meanwhile, Carter questions Cal's trustworthiness after Moss warns her about the detective.
The new Number is an old man, Lou Mitchell, who blows thousands of dollars each week while gambling at a New Jersey casino. While Finch and Reese try to work out how Lou does it, and why he's in danger, Carter helps a fellow detective framed by HR.
Finch goes undercover as an IT worker to get close to their new Number: a VP of technology. However, when she's framed for corporate espionage, Reese and Finch have to take a direct hand to save her life. Meanwhile, Carter demands answers from Cal about his involvement in Szymanski's murder.
Reese and Carter are both racing against the clock. While Reese tries to help a doctor get revenge on the man who gave him a slow-acting incurable poison, Carter must take a stand when IAB goes after Fusco for the murder of his partner, Stills.
After ten days of silence because of the Decima virus, The Machine sends Finch and Reese the Number of an elusive tech company CEO. They soon discover that The Machine is engaged in a last-ditch effort to save itself, and Finch is forced to team up with Root while Reese works with Sam.
Reese and Finch team up with surprising allies in a race to save The Machine from Root and the mysterious international organization Decima, who have both re-emerged with dangerous agendas. As the POI team faces off against enemies old and new, the nature of Finch's relationship with former partner Nathan Ingram is revealed along with his original motivation for wanting to save The Machine's irrelevant numbers. Meanwhile, in her mission to bring Cal Beecher's murderer to justice, Detective Carter finds herself up against the criminal organization known as HR.