Sojourner "Jo" Mullein returns to her hometown of Evergreen, Nevada after her divorce to DEO agent Cameron Chase and reunites with her friends Hal Jordan (a toy salesman) and John Stewart (an architect who takes Jo on at his firm). One day, the town becomes encased in an impenetrable green dome generated by a green lantern-shaped vessel hovering high above. The vessel's master, an alien identifying himself as Abin Sur, descends to the town and orders the townspeople to "be without fear". Abin Sur proceeds to pass "judgment" on the town, seemingly obliterating the citizens one by one, starting with Sheriff Guy Gardner. In the chaos, Hal takes a gun belonging to Guy's deputy Rita, whom the Abin Sur beheads.
As the days go by, John investigates the dome, noting that a faux gold earring belonging by a biker who crashed into the dome somehow passed right through. John eventually concludes that the green energy is vulnerable to gold, or anything taking the form of gold, comparing the alien power to the Philosopher's Stone. Abin Sur sees John's efforts and passes judgment on him. Spurred by John's apparent death, Hal paints the bullets of Rita's gun yellow. With only three of them remaining, Jo confronts Abin Sur while Hal and Todd Rice, the local coffee shop owner, lie in wait to shoot him. During their conversation, Abin Sur reveals that he killed only Rita; those who were "judged" were sent into the Green Lantern to await further judgment in OA (Omega-Alpha), and he tells her to fear the Weaponers of Qard. As Abin Sur leaves, Jo reaches out to him with her left hand, bearing her gold wedding ring, inadvertently disrupting his power and transferring it to her ring. Without Abin Sur to power it, the dome disspates and the Green Lantern falls, crushing Evergreen.
Enraged and grieved and unable to find Jo, Hal shoots Abin Sur with the gold-painted bullets repeatedly. As he dies, Abin Sur passes judgment on Hal by fusing the gun to his hand, cursing Hal with the power of the Black Hand, which drains life and energy. As he melts away, Abin Sur tells Hal to be with fear, to fear the Black Hand and the Black Star. Hal is left with the Black Hand and is constantly seeing a vision of a ring of light with a strange voice telling him to be without fear. Terrified, he leaves Evergreen and happens upon a diner; the Black Hand takes control and consumes the diner patrons and a cop Hal met on the way. Jo arrives, imbued with the power of Abin Sur's Green Flame, also guided by visions of a ring of light. Jo tries and fails to help Hal control his new power; the Black Hand overtakes him and seeks to consume Jo. Meanwhile, Evergreen and the Green Lantern are seized by Hector Hammond, an egomaniacal billionaire with Carol Ferris as his assistant. Hammond captures Todd, Evergreen's only survivor, for interrogation. Jo manages to overcome the Black Hand, pulling both her and Hal into the Green Lantern.
Inside the Lantern, they are met with John Stewart, who has been made aware of their situation. Abin Sur was an Oan, a follower of the four flames in the Enlightenment Spectrum: Qard (black, chaotic action), Rao (red, restraint), Sur (green, correct action), and Aur (gold, understanding/enlightenment). John was given the power of Aur for deducing how the system works, while Guy was given the power of Rao for the mercy he showed Abin Sur; the 2,000 remaining people of Evergreen have yet to be judged. John explains that the Blackstars, a vast cosmic army, see Qard as the highest level and seek to spread their might throughout the universe. Mogo, a sentient Blackstar planet, is coming to Earth. As a "Tomar" (anomaly), Jo purges Hal of the Black Hand and flees Evergreen with him, releasing a large amount of black sludge that Hammond's team confiscates. Jo takes Hal to the Coast City apartment of Cameron Chase, her ex-wife. John relocates the Green Lantern to the Moon.
After the Blackstars, driven by the sadistic Kilowog, slaughter Oans and destroy a planet, they are intercepted by Re of Xudar, a Tomar who stole the power of Rao. Re effortlessly kills Kilowog and sends his remains to Sin Es Tro, Controller of MU (Maker-Unmaker) and leader of the Blackstars.
Flasbacks trace Jo's life from childhood, when she moved to Evergreen as a child with her conservative father Thomas. As an adult, she became a police officer, but quit and left town after discovering Sheriff Bill Hand was a racist who ran a protection racket. After coming out as bisexual in Coast City, Jo met and fell for Cameron Chase, but Cameron's workaholism prevented them from having a steady relationship. The two hastily got married, but nothing changed, so Jo had an affair with former colleague Renee Montoya. After admitting the affair, the two divorced, and Jo moved back to Evergreen after Thomas' passing.
In the present, Jo keeps an unconscious Hal in Cameron's apartment; Cameron contacts Simon Baz, who is put on the Evergreen case with Kari Limbo, a low-level psychic. Hammond interrogates Todd, learning of Jo and her weakness to gold, so he sends his best assassin, Keith Kenyon, after her. After murdering scientist Steven Dayton for Hammond, Kenyon arms himself with a golden suit and gun (dubbing himself "Goldface") before finding Jo and shooting her. Unable to use her powers, Jo performs self-surgery to remove the bullets and kill Goldface before her powers return and heal her. She convenes with Cameron, Simon, and Kari, who uses her powers to trace Kenyon's connection to Hammond. The group go on the run. After Hal wakes up, Kari performs a reading on Jo's ring, learning that Sin Es Tro is being influenced by a "soulless" mechanical being called the "Face of Steel".
Hammond next exposes Todd to the remains of Abin Sur and the Black Hand, mutating Todd into a powerful, mindless beast made of black rock which Hammond dubs "Obsidian". He puppets Obsidian using Dayton's psychic helmet and sends it after Jo, killing Kari. Jo fights Obsidian before Hal, still connected to Qard, reframes the power of "chaotic action" as love, unlocking a Magenta Flame and freeing Todd. Re arrives on Earth, having commandeered the Green Lantern from John, and offers Jo to come with him and take down Mogo.
