The opening scene of this episode shows Lady Une and Colonel Treize walking to meet Zechs and Lucrezia Noin at OZ's main base. Lady Une is obviously jealous of Treize's attentions toward the two and this shows most clearly when the Colonel congratulates and thanks Zechs and Noin. Treize then asks to have a private conversation with Zechs where Zechs asks to work for him a bit longer. Treize then asks why Zechs doesn't take his mask off - his revenge is completed - wherein Zechs replies that he has not yet finished his vengeance.
We zoom in that same base to Lady Une who is in charge of transporting mobile suits. She anticipates a Gundam attack and so we see a briefing on the strengths/weaknesses of each Gundam. Lady Une also tells Zechs (who is now a Colonel) to attack one of the Gundams (the one with Heero inside) alone in the Tallgeese. Noin is shocked at the order and asks to help him. Lady Une tells Noin that she has to stay with her as an adjunct.
We jump to Relena's school where her classmates tell her that Duo and Heero just transferred out. Relena knows they're out on another mission.
The Gundams are now poised and ready to attack. Quatre locates and strikes an OZ train but it turns out to be a trap: the train is filled with ready-to-fight Specials units. The Specials almost get the best of Quatre when Heero jumps into the scene, saving the day.
Meanwhile, Zechs attacks Heero's Gundam and Zechs drops his long-range attack weapon and takes out a sword. He wants the Gundams to duel. Heero accepts the challenge but part-way into the fight, Lady Une makes a stunning move that's not very unlike her. She declares that she has missiles pointed to all the space colonies and will blow them all up unless the Gundams surrender. Zechs is stunned and horrified, stopping the duel.
Coming on to every monitor, we see Dr. J's face appear. He informs everyone that he has been the only one fighting OZ - not the colonies as they once thought - and that he surrenders but will not give up the Gundams. Lady Une tracks the message.
Heero, of course, interpreted Dr. J's message to mean self-destruction. He steps out of his Gundam, right before a stunned Zechs, and explodes it, sending himself falling to the ground below. He looks dead...
Trowa picks up Heero's body and him with the other Gundams leave the scene.
The final scene shows Lucrezia Noin on the phone with Treize - she relays the message to Une to act more elegantly next time. Une is distraught.