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 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.