Meanwhile, word of Lotor's troubles reach the Drule Empire and Keezor is unsympathetic to his plight. And indeed feels they should dispose of Zarkon if he can do no better against Arus than his son.
On Arus, the VF and the leaders of the other planets are plotting to finally do something pro-active in their own defense. They're going to raid planet Doom itself. But it's not as easy as it sounds. A protective field guards Doom, so Voltron just can't fly down and kick butt. But now that they have the canon, they feel they can use it to destroy that barrier. They feel they have no choice given news that the Drules are plotting a massive attack on all Alliance planets and forces. It's also revealed that the Castle of Lions can turn into a rocket ship.
During the meeting, alarms blare. It's Zarkon himself, coming to destroy the canon before they can use it to attack Doom. While the others attack in their Lions, Lance tries to make it to the canon on foot. The plan is discovered and Zarkon tries desperately to stop Lance. Keith lands and tries to help a wounded Lance. Luckily, the castle fires on Zarkon before he can deliver the final blow to the canon. Coran decides to convert the castle into the space ship to buoy the effort. Zarkon has no choice but to retreat. Keezor, back on Drule, is not impressed with Zarkon's duck and run tactics. He then orders the release of Lotor and declares Lotor may punish Zarkon in any way he deems fitting. Mogor frees Lotor, who is delighted to be able to exact revenge on Zarkon. Haggar warns Lotor that the Alliance is getting ready to attack them, so Lotor's idea is to have her build a robeast fit for a King to be imprisoned in. The Robeast, built to resemble Zarkon, is finished just as The Voltron Force nears Doom. The canon is fired clearing a way for Voltron to reach the surface.