Ferris Aircraft's test pilot Hal Jordan (Christopher Meloni) is recruited to join the Green Lantern Corps after the death of Abin Sur. He is placed under the supervision of respected senior officer Sinestro(Victor Garber), who is investigating Abin's murder. Abin was killed while doing an undercover investigation of Kanjar Ro (Kurtwood Smith), who managed to locate and steal the yellow element. What no one realizes is that Sinestro provided Kanjar with the location of the element, in order to have it fashioned into a weapon of comparable power to the Green Lantern battery.
It is revealed that before any other sentient beings existed in the universe, the Guardians of the Universe harnessed the power of the green element, the greatest power in the universe, to create the Green Lantern battery. However, the battery had a flaw: the color yellow, the one part of the light spectrum that can resist green. The most concentrated source of yellow energy, the yellow element, was hidden by the Guardians to prevent others from using it against them.
Jordan quickly comes to understand that Sinestro's beliefs are not in line with those of the Guardians: Sinestro believes that the Guardians have reduced the Corps to merely picking up the messes criminals create as opposed to proactively dealing with the problem. During a mission to capture Kanjar Ro, Jordan is knocked unconscious by Kanjar's energy staff. Sinestro comes in and kills Kanjar, pinning the blame on Jordan. Jordan is stripped of his ring as punishment.
While Jordan waits to be taken home, Sinestro uses his ring to temporarily animate Kanjar's corpse allowing him to learn the location of Qward, where the yellow element weapon is being fashioned. Jordan convinces fellow Lanterns Boodikka and Kilowog that Sinestro is not what he seems. They catch Sinestro red-handed, but Boodikka turns out to be in league with Sinestro and attacks Jordan and Kilowog. Sinestro escapes, and Boodikka is killed when Jordan tricks her into destroying Kanjar's unstable energy staff.
On Qward, the Weaponers bestow Sinestro with the yellow ring and battery. Using its power, he lays waste to Oa, the yellow light easily overcoming the Green Lantern rings. The yellow battery destroys the green battery, rendering all the Green Lantern Corps' power rings inert and causing death by asphyxiation of countless Green Lanterns including Tomar Re and General Kreon, who were in space at the time when their rings failed. Jordan, having recovered his ring moments too late, pounds on the inert green element, breaking it and absorbing the whole of its power. Imbued with the full might of the green energy, he destroys the yellow battery by smashing it between two moons.
However, having exhausted most of his power to destroy the yellow battery, Jordan is left weakened against Sinestro. After a pitched battle, Jordan uses the last of his power to knock Sinestro to the surface of Oa, where Kilowog crushes the yellow ring (as well as Sinestro's hand) with his foot. Kilowog having his ring regained some of its power, then saves Jordan in time.
Once Oa is rebuilt and the Green Lantern battery restored, Jordan is asked by the Guardians to lead the Corps in reciting the Green Lantern oath and Ganthet is put in charge of the Guardians of the Universe by Appa Ali Apsa. Hal Jordan then leaves for Earth to check in with his other boss, Carol Ferris, remarking on the long "commute".