Former Marine and Medal of Honor recipient John Stewart, Aldis Hodge, struggles with civilian life after serving as a sniper in Afghanistan when he witnesses Ganthet's spaceship crash nearby. Ganthet dies of his injuries, and the Power Ring he carries — previously owned by Hal Jordan Nolan North — snaps onto Stewart's finger and pulls him through space to the Justice League Watchtower. There, Stewart encounters Green Arrow Jimmi Simpson, Vixen Keesha Sharp, and Martian Manhunter Ike Amadi, who have been monitoring a disturbance in the cosmos. With the Guardians of the Universe unresponsive and Jordan presumed dead, the trio of allies decides to press onward, using Ganthet's repaired ship to reach the ancient outpost of Oa.
On Oa, they find the Green Lantern Corps slaughtered and the citadel in ruins. Hawkgirl Jamie Gray Hyder appears, warning that security footage shows a Rannian ship docking at Oa just before the attack. She explains that a tenuous peace between Thanagar and Rann had just collapsed, with Jordan overseeing a joint Zeta-Beam project meant to benefit both planets. The test initially worked, but it went haywire, dragging Thanagar into Rann's atmosphere, reigniting the war, and apparently killing Jordan and thousands of others. Stewart and Green Arrow resolve to uncover the truth behind the sabotage and the sudden spike in hostilities.
The team relocates to a Rannian military outpost that was raided by Thanagarians, where they meet Adam Strange [Brian Bloom], thought dead but teleported by the erratic pull of Zeta-Beams. Strange guides them to Rannian High Command, now locked in a skirmish with Thanagar forces. Rannian Captain Kantus reveals Sardath [Simon Templeman], Strange's father-in-law, has repurposed the Zeta-Beam project into a doomsday weapon intended to annihilate Thanagar. Reviewing past footage, Shayera Hol and Strange uncover that a third party has been manipulating both sides for their own ends, complicating the war even further.
Pursuing the impostor ships leads the team to a hidden base inside an asteroid, where they clash with a cadre of Yellow Lanterns and a group of galactic assassins — including Lord Damyn, Kanjar Ro, and Despero — before being captured by their leader Sinestro Rick D. Wasserman. The dark truth surfaces: Hal Jordan is alive, having been captured and infected with the Parallax Entity by Sinestro, and Jordan has seized the remaining Lantern rings to reach a godlike power. The captured crew escapes as Sinestro and his Lanterns pivot to attack Rann in search of Sardath's weapon.
Armed with Sardath's data, the team pursues their escape to Sardath's base, but Sinestro's forces close in. In the ensuing battle, Jordan kills Sardath and reveals the extent of his corruption, cemented by Parallax’s invasion. Stewart and Green Arrow watch in horror as Jordan massacres two of Sinestro's assassins, raising uneasy questions about trust and the true cost of victory. The confrontation crescendos when Jordan finally crushes Sardath’s last defense, and Sinestro’s ambitions threaten to rewrite the balance of power across the galaxy.
As the Zeta-Beam data is secured, Jordan’s grip on power tightens, and he launches another bid to dominate Rann and Thanagar. Strange incurs a bold act, teleporting the weapon elsewhere to protect innocent lives, but the immediate danger remains. Stewart and Green Arrow—each fueled by a sense of responsibility—return to Earth, where Stewart distributes the Green Lantern rings to new wearers, intent on rebuilding the Corps and keeping the peace between the two war-torn worlds. Hawkgirl departs with Ganthet's ship, vowing to reunite with them when the time is right to help guide a hopeful ceasefire.
Back on Earth, a final toast seals the resolve: Stewart proposes dinner and a toast to “absent friends,” a line that lingers in the air as Green Arrow adds with a wry smile, “and maybe a few new ones.”
