Coil guns aimed at each other, Miles, Monroe and Nora are in the midst of their standoff, deep in the bowels of The Tower. Suddenly, five of The Tower's denizens, whom we'll call Dwellers, show up and start shooting. Deciding it's time to work together, the threesome return fire until they're able to run... straight through a door into a water treatment tunnel with the Dwellers close on their heels. They explode several pipes, resulting in a rush of white water, which separates Nora from Miles and Monroe. Deeper in The Tower, Randall enters a bunker and breaks the glass on a portrait of George W. Bush to retrieve a distinctive-looking keycard.
A Dweller uses her keycard to access the Nest (living quarters), where Grace and Rachel are arguing over the risks of shutting down the nanites, which Rachel claims are replicating out of control. Referring to Miles, Monroe and Nora, Jenkins announces that their "friends are gone"; if Rachel tries to access Level 12 to turn the power on, he'll kill her. After taking control of Monroe's encampment, Neville tells loyalist Major Franklin that he's free to leave, then shoots him in cold blood. When the gunshots bring Jason and another guard running, Neville claims Franklin took a shot at him.
When Miles comes to, he finds himself on a lakeshore with Monroe standing over him ready to pounce. The former best friends are brawling when shots ring out - a Militia scout is trying to pick them off! Monroe orders the soldier to hold his fire, but he takes one last shot before running away, and by that time, Miles has disappeared. Monroe flashes back to better days, 10 years after the Blackout, when he and Miles were hanging out in a bar having fun, just before a bomb explodes, destroying the place and severely injuring Miles.
After poking around The Tower's computers, Aaron grows very upset. Grace confirms that he wrote the code that the Department of Defense bought to use for The Tower's operating system. Why does Aaron think Ben Matheson sought him out in the first place? Outside, Neville has stacked a pile of C-4 against The Tower's door. Jason is stunned to learn his father intends to prevent Rachel from turning on the power at all costs. When Jason comments that his father switched sides on a dime, Neville appeals to him for help. He knows Jason hates him; but they're alone, and they need to work together or perish. Without agreeing to anything, Jason says that whatever happens, he needs Charlie and Rachel to stay alive. That's when the Militia scout runs up to announce that he's spotted Monroe in the woods.
Down in the Nest, Rachel tells Grace about Danny, who was born three months early with undeveloped lungs. She loved him instantly and fought so hard for his life that she never stopped. Now her intention is to stop the Militia and set things right, so Danny didn't die for nothing. That's why she's appealing to Grace, who also lost a child. After all, the odds of things going wrong are one in a billion. When Grace stands firm, Rachel chloroforms her, grabs her keycard, and locks her in a room, then joins Charlie and Aaron, who have clearly been in on the plan from the jump.
Walking through the woods, Miles flashes back to 10 years after the Blackout, when he woke up in Independence Hall after the explosion in the bar. Monroe and Nora tell him the Rebels planted the bomb, as part of their cockamamie plan to bring back the United States. Monroe brings Miles to the window to watch five coffins being loaded into a wagon. Not only did Monroe kill the bomber, but he killed his family, with the intention of making him an example. Back at The Tower, Aaron tells Rachel and Charlie that he built a back door into his code - and it's open. Furthermore, he thinks the Blackout wasn't an accident. Someone did it on purpose. That's when Nora shows up to say she has no idea where Miles is. And in that moment, she knows Rachel loves Miles - and he loves her back. Miles will choose Rachel every time.
Miles is walking through a field when Monroe attacks him again. Miles makes quick work of Monroe, then walks away, refusing to stay and fight. Monroe accuses him of starting "all of this," then brings up the night Miles tried to kill him in his bed. Miles claims the reason he abandoned Monroe was about a lot of things, like the time he killed the Rebels. Monroe insists everything he ever did was for Miles. Suddenly, the two men hear a Militia chopper, which starts shooting at them. They make a run for it, and the next thing Monroe knows is the sensation of a rifle butt hitting his head. Later that night, Miles watches from the cover of trees as Monroe is dragged before Neville in chains.
Neville tasks his Militia men with blowing up the concrete around The Tower door while he toys with Monroe, whom he feels has become deranged with a borderline erotic obsession with Miles. Neville can't just shoot Monroe as he'd like; he's going to have to at least create some semblance of a trial. According to Neville, the difference between him and his former boss is that Monroe frightens, whereas Neville inspires. Monroe is surprised to see Jason alive when he reports the men have blown an opening under The Tower door. Once the Nevilles have left for The Tower, someone enters the tent to rescue Monroe. Miles admits he can't kill Monroe because they're still brothers. Urging him to run, Miles betrays Monroe seconds after freeing him, screaming, "Monroe's escaping!"
Jenkins and his Dwellers manage to step around a trip wire Nora has set to trigger a bomb. Nora throws a fire extinguisher to set off the bomb, badly wounding herself in the process. With Nora bleeding out, Aaron and Charlie want to use the stolen keycard to bring her to the infirmary, but Rachel and Nora agree they need to use the keycard to get to the 12th floor. They have to turn the power on for Danny. Charlie points out that Danny's dead; Charlie's alive and she needs her mother's help. Rachel tells her to lock the door and wait for her return. Furthermore, Rachel needs Aaron to come with her because he's the only one who can program The Tower's computers. When Nora tells him to go, Aaron complies.
Nora's screams draw one of Neville's Militia men, who bashes through the locked door. Charlie puts up a good fight, but just as the soldier is getting the best of her, Miles shows up to slit the guy's neck. Miles refuses to leave Nora, who insists Rachel needs him more. Miles scoops Nora into his arms, and Charlie leads him to the infirmary; but Nora dies on the way. Devastated, Miles sobs before giving Nora one last kiss. Within moments, Miles pulls himself together, knowing full well that Neville and the Militia are on their way to intercept Aaron and Rachel on Level 12.
Charlie and Miles ambush Neville and his men. After a fierce firefight, Aaron, Rachel, Charlie and Miles find themselves in Mission Control. Aaron hops on a computer and gets to work. Rachel calls the shots as an incensed Neville sends a man to retrieve the rest of the C-4. His intention is to kill the foursome trying to restore the power. At the point of executing the final bit of code, Aaron pauses. What if Grace is right? What if they destroy the world? Rachel assures him they won't, so Aaron hits the enter key. Slowly but surely, the lights flicker on all over the world as the power is restored. In Atlanta, President Kelly Foster gives the command to sic all Georgia's tanks and choppers on Philadelphia.
Monroe is outside on an open plain when a wild, unnatural lightning storm starts. Randall shoots the keypad outside Mission Control, locking Rachel et al inside. Miles immediately tries shooting out the bulletproof glass to no avail. Apparently, Rachel has played right into Randall's hands. The reason he wanted the power on? For an immediate launch of ballistic missiles at Atlanta and Philadelphia. After hitting the launch button, Randall shoots out the controls - there's no turning back. He never cared about Monroe; Randall merely wanted him to wipe out Georgia, so he could wipe out Monroe. Once the most powerful capitals were gone, Randall would be free to unite the United States, bringing back its "real leaders." Randall raises his hand in salute to his own patriotism, then raises his gun to his head.
With Randall dead, all Aaron, Charlie, Miles and Rachel can do is watch with horror as the missiles close in on their destinations. Meanwhile, somewhere on a base at the United States colony of Guantanamo Bay, Cuba, un unseen man chuckles while turning a lamp on then off, on and off. An aide steps into the office to report that Randall Flynn finally "did it." Now it's time for the President of the United States to go home...
The struggle to turn on the power culminates in the explosive season finale! Leslie Hope and Kim Raver guest star.