It's been three months since Rachel, Aaron, Charlie and Miles tried to stop the bombs from hitting the East Coast. They weren't successful. Philadelphia and Atlanta are dead zones, pits of darkness marked by only a few pockets of desperate humanity. Somewhere in the Plains Nation, Charlie sits in a raucous roadhouse, flirting with a bartender named Jeff. Without much hesitation, she slips into a back room with him and the two hook up, just trying to escape from it all. Noticing the Monroe brand on Charlie's arm, Jeff mentions he saw Monroe a couple weeks back. With this kernel of information, Charlie sets out to find him with an air of desperate determination.
In Willoughby, Texas, a bloody Miles burns down a shed in a field, then visits Rachel, who's now helping her father, Dr. Gene Porter, operate a small clinic out of his home. Miles' hand is badly cut, and he's in severe need of medical attention. Dr. Porter patches Miles up and warns him to stay away from Rachel. She's been compulsively trying to pin down Randall's motivations for the bombing, and despite her lack of success, she's finally healing emotionally; the last thing she needs right now is the wrong guy.
Elsewhere in Willoughby, Aaron is comforted at home by his new girlfriend, Cynthia. She's optimistic about the future of the world - after all, the lights came on right before the bombings, if only for a second - but Aaron is more pessimistic. While gathering firewood, Aaron is enveloped in a sea of fireflies... and has an epiphany about the biological energy capabilities in nature.
In Savannah, Georgia, Neville and his son Jason case through an endless refugee camp in search of Julia. But Neville realizes they will never find Julia, as she was too loyal to have ever left Atlanta. She would've waited for her family. The thought of her death crushes Neville. He puts a gun to his head, but Jason talks him down. A commotion outside causes the two to leave their tent. A beautiful schooner is docking at the harbor, flying the old Stars and Stripes. Later, Secretary Justine Allenford gives a speech on shore about how the U.S. government is back to help its people, and the President is on his way to the White House as she speaks. Everyone is excited... except for Neville. He's convinced these people were behind the bombings - and if they were, he vows to seek vengeance for the death of his wife.
As Miles prepares to leave Willoughby for good, Rachel all but begs him to stay. He can't though; bad things happen when those two are together. On his way out of town, Miles witnesses a family being attacked by menacing figures outside their farmhouse. He rushes to rid the innocent people of their assailants and is met in a cornfield by one of the attackers. A tussle ensues, and Miles manages to slit the guy's throat with his sword. Miles stumbles to his feet, wondering who the heck these guys are.
Charlie finds Monroe in an entertainment encampment called New Vegas, where he's making money as a bare-knuckled boxer. Charlie stalks him from a distance, trying to dig up information on his whereabouts and routines. She gets a carny to lure Monroe out of his trailer in hopes of meeting "a girl," but on his way to the bar, Charlie fires an arrow at him, hoping to kill him. At the same time, two men attack Monroe, knock him out and drag him into the woods. Charlie's arrow misses, and she's left wondering what the heck is going on.
Aaron goes to Rachel with his thoughts about the fireflies, which she tries to write off as nothing. Aaron knows things have been really weird ever since the bombs dropped, for the two of them especially. Before Rachel can respond, Miles walks into town, a dead man strapped to his horse. Miles tells the sheriff they're dealing with a war clan, and a large-scale attack on the townspeople is imminent. The sheriff rushes to call in reinforcements, and Miles realizes he can't walk away from his past as easily as he had hoped. Later on, a war clan member attacks Cynthia in her home, and when Aaron rushes to save her, he's slashed through the chest with a machete. Rachel tries to save him with the help of her father, but Aaron's lost too much blood. He dies; everyone in the room is devastated.
Outside, Miles fights off a group of bandits attacking another set of townsfolk. He saves their lives, but soon realizes he's far outnumbered. Miles and the sheriff are taken to the war clan's base, where they meet the tribe's leader, Titus Andover, who is another whole level of creepy. Whatever's about to go down is not good.
Rachel and her father console a grieving Cynthia. She can't believe Aaron is gone. Suddenly, fireflies overheard temporarily mesmerize her; they're so enchanting and full of energy in a blacked out world. Inside, Aaron lies lifeless on the floor. And then suddenly, he GASPS.