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.