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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 Root both gain access to The Machine, thwarting Decima. However, Root takes Finch captive as part of her plan to find The Machine and set it free. Reese and his new ally Sam Shaw must track Finch down and avoid Decima. Meanwhile, Carter tries to find Cal's killers, and Finch remembers what happened to his partner, Nathan Ingram.
Reese and Finch work with their new partner, Sam Shaw, to track down a sailor on leave who is the next Number. Meanwhile, Carter deals with her demotion to beat cop, and Root makes herself at home in the sanitarium.
The newest Number is CEO Wayne Kruger, who makes his living brokering personal data. However, when someone starts exposing his personal life and all of its dirty secrets, Kruger vows to get revenge. Meanwhile, Carter puts up with a new partner.
The team's newest Number is a wealth young businessman who stalks women, and may be connected to the death of one woman in particular. To lure him into making a move, Finch calls in Zoe to help Carter and Sam link up with the man. Meanwhile, Root plans her escape from the institution with some help from her unseen ally.
The team's new Number is a New York lawyer under arrest for the murder of her husband, who supposedly disappeared at sea without a trace. The lawyer quickly escape jail and goes on the run, and the team has to track her down and determine if she's victim or perpetrator.
The group's newest Number is a 10-year-old immigrant girl who has stumbled onto a massive drug-manufacturing operation... with ties to HR. Sam goes on the run with the girl but soon loses her, and vows to get her back no matter what. Meanwhile, Carter's life is at risk when her partner Laskey makes his move on behalf of HR.
While Finch tries to protect an estate investigator whose Number has gone up, Reese searches for a missing Sam... unaware that Root has convinced Sam to help with a mission for The Machine. Meanwhile, Carter teaches Laskey about the reality of how HR operates.
The Machine sends the team the Number of a conman who claims to be a hypnotherapist and uses the information he obtains to access his patients' bank accounts. However, it turns out that one of the patients is a money launderer for HR... and they're not too happy to learn that someone is ripping them off.
The Machine gives Finch thirty-eight Numbers, and he realizes that someone is planning to set off a war between HR and their Russian Mob allies. Meanwhile, Carter continues her own investigation into HR and remembers her past with her ex-husband.
As Carter and Reese try to turn the head of HR over to the Feds, they discover that the organization has set up roadblocks and cut off every means of access. Finch tries to rally the the troops to help them, and is forced to turn to an unlikely ally who demands a high price for her assistance.
The hunt is on for Simmons after he kills one of the team. Finch and the others try to stop Reese from killing the crooked cop on the run, but soon realize that he's not the only one who wants Simmons dead.
With Reese and Fusco absent, Sam and Finch take on a new Number: a man dying of a brain tumor. In the past, a young Finch pursues his interest in computers.
Finch and Sam try to recover the Samaritan drives from where Arthur hid them, but Vigilance and Control's team move in on them, cutting off their escape. Meanwhile, Control interrogates Root and gets unexpected answers, while Fusco tries to convince Reese to come home.
Reese tries to leave the country after Carter's death, but The Machine manipulates him into saving a Number... who may also be a "relevant."
No sooner has Reese returned to New York then the team finds itself helping a thief with an interest in rare antiquities... and keeping a loved one safe.
The team's newest Number is a 911 operator, Sandra. Finch signs on at her call center as a trainee and soon learns that a mysterious caller plans to have Sandra erase valuable files... and will kill a young hostage if she doesn't.
In 2010, Finch and his enforcer help their newest Number, a programmer who two CIA agents want dead.
The paths of Root and the team coincide when the Machine sends them all to protect a janitor who is wanted by both Vigilance and Decima.
While Decima gathers its resources to build a new Machine, the team receive the Number of an electrical engineer who is caught up in UN intrigue trying to help an Iraqi translator receive asylum in the U.S.
Finch sends Reese and Sam to a high school reunion to protect their new Number, while he travels to DC with Fusco to look more closely into the death of their last Number at the hands of Vigilance.
Finch calls Reese to Washington to help protect their new Number, a U.S. Senator. However, they soon discover that the people that they may have to protect the senator from are... themselves.
Samaritan goes online for 24 hours, monitoring New York City, and Greer uses the opportunity to find Reese, Sam, and Root. At the same time, he has his people try to locate anyone with a connection to the missing Finch... and comes up with Grace Hendricks.
The Machine predicts a major upheaval coming and sends Root to work with Reese and Sam to get it the intel it needs. Meanwhile, Greer talks with Finch, and Vigilance makes its move as Collier's hatred for the government is explored.
While Reese and Hersh try to track down Finch, who is on trial by Vigilance, Sam helps Root sabotage Samaritan. Meanwhile, Finch has no choice but to confess that he created the Machine and defend his actions.