Long ago, the Guardians of the Universe, the first sentient beings to exist, harnessed the power of the green element to forge the Green Lantern battery. However, the battery was vulnerable to the color yellow, the one part of the light spectrum that could resist green. To shield against this weakness, the Guardians hid the most concentrated source of yellow energy—the yellow element—away from prying hands.
After Abin Sur's death, a group of Green Lanterns arrives to recruit Ferris Aircraft's test pilot Hal Jordan, [Christopher Meloni], to the Green Lantern Corps on Oa. The mission is overseen by Sinestro, [Victor Garber], who is already probing Abin Sur's murder. Unbeknownst to the others, Sinestro had secretly shared the location of the yellow element with Kanjar Ro, the formidable foe whose ship the Lanterns briefly board in search of the weapon’s whereabouts, [Kurtwood Smith]. Abin Sur had come under attack during that undercover pursuit, and upon crashing back to Earth, Jordan learns that his ring may be the Corps’ last line of defense against a threat far greater than he realized.
Jordan quickly grasps that Sinestro's philosophy diverges from the Guardians’ ideals: where the Guardians want to proactively face danger, Sinestro contends that the Corps should prevent crime by any means necessary. During a mission to capture Kanjar Ro, Jordan is knocked unconscious by Kanjar Ro's energy staff. Sinestro arrives, kills Kanjar Ro, and blames Jordan for the incident. As punishment, the Guardians strip Jordan of his ring, leaving him stranded while the fleet adapts to the new threat.
While Jordan waits for transport home, Sinestro uses his ring to temporarily animate Kanjar Ro’s corpse, hoping to learn the location of Qward where the yellow weapon is being forged. Jordan convinces fellow Lanterns Tricia Helfer as Boodikka and Michael Madsen as Kilowog that Sinestro cannot be trusted. When they confront Sinestro, Boodikka reveals her true allegiance and incapacitates Kilowog, allowing Sinestro to escape. In a desperate gambit, Jordan tricks Boodikka into destroying Kanjar Ro's unstable energy staff, and the resulting explosion sends her careening into the tools hanging above, killing her.
On Qward, the Weaponers grant Sinestro a yellow ring and battery, equipping him with a power that can outpace the Green Lanterns. With this new weapon, he devastates Oa, the yellow light overpowering the green rings and destroying the green battery. The green rings go inert, and many Lanterns in space perish from asphyxiation as their power drains away. Jordan, having recovered his ring moments too late, pounds on the inert green element and, when a crack appears, he presses his own ring onto it, siphoning the green energy anew. Imbued with fresh power, he crushes the yellow battery between two moons, fatally crippling Sinestro’s plan.
Having exhausted most of his green power to neutralize the yellow threat, Jordan faces Sinestro in a brutal, hand-to-hand struggle without the aid of constructs. With the last reserves of energy, Jordan knocks Sinestro to the surface of Oa, where Kilowog finally crushes the yellow ring beneath his boot. Kilowog, having regained some of his own power, soars to the rescue, saving Jordan from a deadly fall and ensuring the Lanterns’ future was not erased in a single stroke of yellow flame.
When Oa is rebuilt and the Green Lantern battery restored, the Guardians grant Jordan the honor of leading the Corps in reciting the Green Lantern oath, marking his acceptance as a true protector of space. With the crisis averted, Jordan departs for Earth to check in with his other boss, Carol Ferris, [Olivia d'Abo], reflecting on the long, winding commute that now defines his remarkable duty.
