Reese & 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.

Reese and Finch realize that a virus has rendered The Machine erratic, causing it to issue numbers irregularly. As they race against the viral countdown, the team searches for a tech millionaire so elusive no one has ever seen him. Also, Detective Carter's mission to bring Cal Beecher's murderer to justice lands her squarely within the sights of the HR criminal organization.

When a luminary in the world of medicine is poisoned, Reese and Finch have just 24 hours to determine the deadly toxin he was given and find the person behind the attack. Meanwhile, Detective Fusco's past corruption catches up with him when an informant gives the Internal Affairs Bureau the crucial information they need to send him to prison.

When the number of a leading tech executive comes up, Finch infiltrates her corporation to gather intel but can't determine whether she is working in her company's best interest or planning to destroy it from the inside. Meanwhile, Carter continues to question Detective Beecher's integrity after he provides incriminating information about a fellow detective.

When an elderly gambler's number comes up, Reese and Finch head to Atlantic City to delve beneath the surface of their POI's seemingly ordinary life for answers. In New York, Carter's crusade to clear a fellow detective's name brings her perilously close to discovering the remaining HR faction within the department.

After The Machine gives Reese and Finch six numbers at once, their search for clues leads them to a coastal town where they are forced to ride out a storm with a group of locals in a police station. However, as the weather rages outside, a sinister situation arises inside when they realize there is an unidentified killer hiding among them.

A lethal and sexy government operative who tracks and stops terrorist threats before they occur finds herself on the run - and the new focus of Reese and Finch's attention. However, their pursuit proves to be their most formidable when they discover that her remarkable skillset equals their own.

Reese and Finch race to save a hotel maid's life but find themselves surrounded by more suspects than they may be able to eliminate when they realize any guest or staff member could be her potential killer. Meanwhile, Detective Carter weighs a major offer from the FBI.

Reese and Finch meet their match in a tech billionaire POI whose curiosity and limitless resources threaten to expose their identities and sabotage their efforts to save his life.

Reese is abducted by an old acquaintance planning a massive act of cyber-warfare that could lead to Reese's death.

While Carter engages in mental warfare with the FBI to help Reese evade Agent Donnelly's narrowing focus, Reese crosses paths with foes both old and new. Meanwhile, Det. Fusco is forced to fly solo to help the team's newest POI: supermodel Karolina Kurkova.

Finch goes undercover as a high school substitute teacher to protect a teen genius POI as Carter undertakes a dangerous mission to stop the FBI from determining that an imprisoned Reese is the "Man In a Suit".

While the FBI refocuses their efforts to catch "The Man in the Suit," Reese's latest POI becomes a personal quest after he learns that she's the sister of a soldier who was killed in action.

Finch and Reese's surveillance skills are pushed to the limit when a New York City cab driver's number comes up and any one of his passengers could be involved in the impending crime.

The team is spread thin when a husband and wife's numbers both come up.

The Machine gives Finch and Reese the number of a brilliant surgeon, but they soon discover that a resourceful third party has raised the stakes for this POI, forcing them to turn to an unlikely source for help.

Reese goes undercover in an idyllic neighborhood when The Machine's latest number sends him to the suburbs.

Reese must protect an investigative journalist through surreptitious means to avoid becoming part of her story.

When The Machine gives them the number of a mob enforcer whose life becomes endangered, Reese and Finch must decide whether to intervene or allow karma to balance the scales of justice. Meanwhile, Finch seeks aid from an unlikely source.

With Finch back in the Library, Reese returns to field work, only to face his toughest case yet - protecting the privileged daughter of a Brazilian diplomat.

The Machine delivers the number of a cold case that leads Reese ever closer to catching up with Finch and his kidnapper, Root.

With Finch missing - kidnapped by his hacker nemesis, Root, in last season's finale cliffhanger - Reese enlists Detectives Carter and Fusco to get his friend back.