In a flash-forward, Walt dines alone at a restaurant on his 52nd birthday, looking gaunt, with a full head of hair and beard. He meets with a gun dealer, who sells him a car with an M60 machine gun in the trunk.
Back in the present, Walt and Jesse convince Mike to help them destroy Gus‘ laptop, which has been confiscated by police and contains security footage from the superlab. They succeed by parking outside the police evidence room with a massive junkyard electromagnet, which also damages a picture frame of Gus’, revealing secret bank account numbers.
Jesse, meanwhile, is preoccupied over the missing ricin cigarette. Walt agrees to help him look for it and stashes a fake in Jesse’s Roomba, having hidden the real vial behind an outlet cover in his own bedroom.
Walt and Jesse make plans to start another meth operation and try to recruit Mike as a third partner. Though Mike initially refuses, he eventually agrees to the scheme when he realizes the DEA has confiscated all the money from Gus’ offshore accounts — money Mike was saving for his granddaughter and as leverage to keep Gus’ now-imprisoned employees from snitching.
Lydia, a Madrigal executive, advises Mike to kill 11 men still on Gus’ payroll before they talk. Mike refuses, so Lydia hires one of the men, Chris, to kill Mike and the ten others. Chris only manages to kill one man — Duane Chow, who ran Gus’ chemical depot — before Mike takes Chris out.
Mike then goes to kill Lydia, but lets her live after learning she has access to methylamine, the key ingredient in Walt’s meth — a move he knows is dangerous, but he’s determined to leave his granddaughter a legacy.
Unable to find a suitable lab, Walt concocts a plan to cook inside houses that are undergoing fumigation by Vamonos Pest. On pay-day, Walt bristles when Mike takes out “hazard pay” for Gus’ remaining nine men. Like Lydia, Walt would prefer that these nine men were dead, not paid off.
As Walt becomes more self-assured, Skyler grows distant and fearful for her family’s safety. To keep Walter, Jr. and Holly away, she fakes an emotional breakdown by walking fully-clothed into the pool during Walt’s 51st birthday party. Hank and Marie agree to take the kids while Skyler and Walt work out their issues.
Afterwards Walt angrily confronts Skyler, who says she’s just waiting for his cancer to return. It’s a slap in the face and a wake-up call for the increasingly ruthless Walt.
The DEA arrests Madrigal’s warehouse foreman responsible for procuring barrels of methylamine. Before her supply dries up entirely, Mike sends Jesse to help Lydia transport the methylamine, but she spots a GPS tracker attached to a barrel. Walt plants a bug in Hank’s office and learns the DEA in Houston has tagged all the barrels.
Realizing that her methylamine is now useless, Lydia tells them about a train carrying 24,000 gallons through New Mexico. They plan an elaborate heist and enlist Todd from Vamonos Pest to help. The heist is successful. However, Todd shoots and kills a boy who accidentally stumbles upon the scene of the robbery.
Rattled by the boy’s death and Hank’s dogged investigation, Jesse and Mike tell Walt that they’re quitting the business. Mike outlines a plan to sell their shares of the methylamine to Declan, a Phoenix connection, for $5 million each. Walt accuses Jesse of selling out.
Declan agrees to buy the methylamine only if he can have all 1,000 gallons, but Walt refuses to sell his share. Instead, Walt comes up with a plan that gives Declan a 35 percent stake in the business if he agrees to distribute the meth and pay Mike $5 million. Declan accepts. Mike parts ways with Jesse and meets with his lawyer, Dan Wachsberger, to ensure his nine men will receive their hazard pay after he skips town.
Jesse reminds Walt that he wants out, too, but Walt refuses to listen. Jesse angrily leaves without collecting his $5 million share. Walt enlists Todd as his new cooking assistant.
Mike’s lawyer is arrested by the DEA, exposing Mike and the nine men in prison.
Walt visits Hank to retrieve the bug and overhears Hank and Gomez mention that Wachsberger has agreed to rat Mike out. Walt warns Mike, who escapes the DEA just in time. Walt delivers a go-bag to Mike and demands the names of Mike’s nine men. They fight and Walt shoots Mike in a fit of rage. Todd helps Walt dispose of Mike’s body.
Walt obtains the names of Mike’s nine men from Lydia. Using Todd’s uncle’s prison connections, Walt orchestrates the simultaneous murders of all nine men. Hank, who was on the verge of getting the men to testify, is devastated.
As time passes business thrives, but Walt grows weary. Months later, Skyler shows Walt a storage unit filled with cash. “How big does this pile have to be?” she asks. Walt visits Jesse. Reminiscing about their early days cooking in the RV, Walt hands over Jesse’s $5 million share. Afterward, at home, Walt tells Skyler he’s quitting the business.
Later, the Whites enjoy a poolside meal with Hank and Marie. Hank uses the bathroom and finds a copy of Walt Whitman’s Leaves of Grass. An inscription reads, “To my other favorite W.W. It’s an honour working with you. Fondly, G.B.”
Hank flashes back to the time he consulted Walt about Gale Boetticher’s lab notebook. Hank reads a note — “To W.W. My Star, My Perfect Silence” — and jokes that the initials correspond with Walt’s. “You got me,” jokes Walt, putting his hands up.
Back in the present, a look of horror crosses Hank’s face as the realization sinks in: Walt is Heisenberg.