The Justice League stand trial on Rimbor for their attack on the planet, and Superman tries to explain that they were under the mind control of Vandal savage. The prosecutor, Galet Dasim, goes on about the atrocities that they committed while the spectators complain about the defendants refusing to pay their bribes. The trial pauses when everyone receives the news that The Reach are attacking Earth. As they wait for the trial to resume, Green Lantern explains to his teammates that The Reach were a vast conquering army that battled the Green Lantern Corps. Eventually the Corps signed a treaty with The Reach, and now they can only invade worlds where they have been invited, and the Corps isn't allowed to interfere.
In one of the galleries, the galactic conqueror Mongul watches the trial and his comrade, Vandal Savage, points out that The Reach's plans on Earth could affect Mongul's own efforts to conquer the galaxy. After considering Savage's words, Mongul walks out.
On the Justice League Watchtower, Captain Atom informs Aquaman and Nightwing that they have detected some massive object approaching Earth. On the planet below, The Reach confirms the object's approach and contacts its owner, Mongul. When the Ambassador informs Mongul that they have claimed earth, Mongul tells him that their presence has attracted his attention.
At STAR Labs in Taos, Green Beetle briefs Nightwing and the others on the object. He explains that it is War world, a massive artificial satellite and mobile weapons platform. Mongul recovered a crystal key that gives him complete mental control of all of the platform's weaponries. The alien has set out to reclaim his homeworld by conquering the entire galaxy, and believes that The Reach's efforts pose a threat to his schemes of conquest.
At ivy Town, Mal and Karen are spending some time together, but she's distracted when she sees War World in the sky above. The massive object disrupts Earth's tidal patterns, causing widespread pattern. At the UN, the Reach Ambassador goes on the news to assure everyone that despite the fact he only has one unarmed ship, the Reach are with the people of Earth in spirit.
Captain Atom attempts to negotiate with Mongul, but the alien explains that he is doing them a mercy by wiping them out quickly rather than let them fall under the control of The Reach. Mongul fires his giant laser emitter at Earth, but Dr. Fate creates a mystic shield and Icon uses her inertia winder to shield him from harm. The League members capable of functioning in space attack War World directly along with Green Beetle, but the attack is a distraction so that Nightwing can send three teams of heroes into War World.
Young Justice enters War World, using Blue Beetle's scarab to blind the security systems and evade detection. Alpha Team goes after Mongul, Beta Team go after the key, and Gamma Squad moves for the power core. Delta Team, Robin and Batgirl, fire on War World from the bioship and try to cover their teammates' presence. Meanwhile, The Reach watches the entire battle and find it ironic that they have to rely on their enemies to save the world they plan to conquer.
The automated security drones within War World soon detect all three teams. Alpha Team--Superboy, Wolf, Arsenal, and Wonder Girl--get to Mongul's control chamber and attack the alien. He comes from a red sun like Superman and is just as strong, and easily casts them aside. Once they are down for the moment, Mongul prepares to launch a massive missile strike now that his laser emitter is destroyed. Dr. Fate and the League try to block the missiles, but The Reach calculates that 23% of them will still impact Earth, rendering the planet unusable for their purposes. They have no choice but to launch their concealed fleet, losing two-thirds of their ships to stop the remaining missiles.
Gamma Squad--Bumblebee, Guardian, and Sphere--reach the power core. Bumblebee and Guardian are bickering back and forth about their relationship, and Guardian tells her to blast the power core. She reminds him that they have to shut it down and flies into the core, and Guardian whispers good luck to her.
Beta Team--Blue Beetle, Impulse, and Beast Boy, get to the key chamber but the drones detect them and open fire. More drones attack Gamma Team, and Bumblebee warns Guardian that the power core keeps rerouting energy as fast as she can redirect it. He irritably tells her to reroute the power to somewhere useful and Bumblebee gets an idea. She reroutes the energy to Mongul, shorting out his telepathic link and deactivating the security drones. Alpha Squad rallies and takes the stunned Mongul down for good, while Guardian and Bumblebee hug in celebration.
Blue Beetle grabs the key, and The Reach, watching through the beetle scarab, are satisfied that they've accomplished a great deal despite the loss of much of their fleet.
As the teams reunite in the hanger, Guardian and Bumblebee congratulate each other and he admits that he's proud of her. Bumblebee apologizes for taking him for granted and they kiss. Alpha Team arrives and Blue Beetle launches an attack of his own. He knocks out impulse first and then goes after the most powerful members, Superboy and Wonder Girl. Arsenal, panicking, refuses to go back into captivity and opens the hanger into space. Blue Beetle is almost swept out but manages to pull himself back in. As Arsenal swings away into War World, Blue Beetle reseals the airlock and subdues the remaining heroes, while The Reach watches in satisfaction.