On Rimbor, Superman speaks before the galactic court, defending his comrades. He insists that they never attacked Rimbor, insisting that they were under mind control. The prosecutor, Galet Dasim, doesn't believe it, while the spectators wonder why the defendants haven't paid the bribes and cleared themselves. Superman admits that he doesn't know why Vandal Savage sent them there to attack Rimbor.
The trial is interrupted when the spectators receive word that The Reach is attacking Earth with plans to conquer it. Green Lantern explains to his comrades that millennia ago it took the entire Green Lantern Corps to stop The Reach, leading to a treaty. Now The Reach can only go to words where they are invited, and the Green Lanterns can't interfere. Meanwhile, the alien conqueror Mongul watches from the gallery and his comrade points out that The Reach's invasion of Earth has long-term implications for who rules the galaxy. Mongul leaves the courtroom while his comrade—Vandal Savage--looks on in satisfaction.
At Watchtower, Captain Atom informs the two teams that they've spotted something huge on a course for Earth.
The Reach and Black Beetle detect the object's approach and the Ambassador contacts it. He informs the new arrival that The Reach has claimed Earth, but Mongul responds and tells them that he has come to Earth because of them.
At Taos, Green Beetle meets with STAR Labs and informs them that the approaching object is War World, a massive artificial satellite and mobile doomsday weapon. It was reactivated by a crystal key that was recovered by Mongul, who now controls the automated satellite via a mind link. Green Beetle explains that Mongul was ousted from his home planet and is now planning to take it back by conquering the entire galaxy, and considers Earth a threat to his plans.
At Ivy Town, Mal and Karen spend some time together, they see War World in the sky. Panic spreads across the Earth as the satellite affects tidal patterns. At the UN, the Ambassador says that they take the threat seriously but claims they only have one unarmed ship.
Captain Atom contacts Mongul to open negotiations, but the conqueror says that he plans to eliminate a Reach-controlled Earth because it endangers his plans. Mongul then opens fire, only for Dr. Fate to reflect the first blast back. The rest of the League and Green Beetle move in to attack while Rocket protects Dr. Fate. Nightwing sends his team inside to strike at War World from within, using Blue Beetle's scarab to bypass the security systems.
Superboy, Wonder Girl, Wolf, and Arsenal on Alpha Squad move in on Mongul. Beta Squad--Blue Beetle, Impulse, and Beast Boy--head to the key chamber. And Gamma Squad--Guardian, Bumblebee, and Sphere--head for the power core. Robin and Batgirl are aboard the bioship and lay down cover fire to divert attention away from their teammates. On Earth, The Reach watches and the ambassador admits that their only chance of success is the League.
Security drones spot all three teams and open fire. Alpha Squad reaches Mongul, who dismisses them as inconsequential. He easily tosses them aside, explaining that he comes from a red sun like a Kryptonian, and then explains that he's trying to grant them mercy by sparing them the domination of The Reach. Mongul then unleashes all of his weapons at Earth.
Dr. Fate attempts to block the missiles but the League's combined forces can only neutralize 77% of the incoming attack. The Reach realizes that they have no choice but to mobilize their fleet and defend Earth. Their ships open fire, attacking the missiles that have gotten past the others and sacrificing two-thirds of their fleet.
Gamma Squad reaches the power core but Bumblebee reminds Guardian that they have to shut down the power core rather than destroy it. She flies to the core and Guardian wishes her luck.
Beta Team gets to the key chamber as a new wave of drones attack. More drones open fire on Guardian and Sphere, while Bumblebee warns that the power in the core keeps rerouting power. He tells her to reroute the power to somewhere useful and Bumblebee gets an idea. She sends the energy into Mongul via the telepathic link and all of the drones go dead. Alpha Squad attacks the stunned alien and tie him up. In the power core room, Guardian and Bumblebee hug.
Blue Beetle takes the key, while The Reach realize that despite the price they've paid, they've acquired a vital component.
As the teams reunite, Guardian admits that Bumblebee saved the day. She points out that it was his idea but he says that she's outgrown him and he's proud of her. Bumblebee admits that she's been taking him for granted and they kiss. As Alpha Team arrives, Blue Beetle knocks out Impulse and attacks the others. He quickly subdues Wonder Girl and Superboy, and Arsenal panics, vowing not to be captured again. He opens the airlock but Blue Beetle manages to reseal it and knock out the others, and only Arsenal manages to escape.