The man explains how Zarkon conquered Philos as it passed Doom, and that Lotor was enslaving his people to build a shrine to Allura there (you know it shows true love when you don't do the work yourself). Zarkon himself shows up to have Lotor arrested for wasting time on a temple to his love. But Lotor quickly explains he's also built a base that'll help conquer Arus.
Zarkon is less than impressed with Lotor's scheme to defeat Voltron using special missiles. Zarkon thinks his Herculean Generator is the better weapon.
On Arus, the escapee happened to be involved in the project for the generator and brought with him blueprints to show the team. The generator looks like a snail and creates whirl winds that pulverize everything in its path. Admittedly, they acknowledge Voltron isn't a match for wind, so their plan is to study the blueprints carefully and fly to the comet/planet before it reaches Arus.
Meanwhile, Zarkon assures Lotor that they'll lure Voltron to his doom by having Merla attack an Alliance fleet. When they come to the rescue, the generator will take out Voltron. The team gets the distress call and are about to launch when the stranger asks Keith if he can come with them to help them navigate Zarkon's defenses. Keith is okay with it, but Lance balks thinking the helpful escapee bit reeks of a Zarkonian plot. The man appeals to Allura's intuition, and she deems him sincere (yeah, her judge of character is right on given she fell for Bokar and other such asshats in disguise in the past lol!). Lance remains unconvinced.
In the skull tank, the mystery man leads the lions onto Philos (finally, we learn his name is Zane). He and three of the Lions go off to try to take out the generator while Keith and Allura find the star cruiser and try to save it from Merla's attack fleet. Merla is turned away, and the two victorious Lions escort the ship out of danger. Meanwhile, Lance still struggles to trust Zane as the alien insists on going about taking out the generator his way. Zane goes ahead and tries to take out the missile defenses alone and it seems he's lost in the battle - but not before he spots the generator and tells the others where it's at. When Keith and Allura show up, Lance admits Zane was a brave guy and that he was wrong about him.
However, time is of the essense because Philos is about ready to fly by Arus. The Lions rush to where Zane told them the generator was...only to be trapped in a mine field. Lance was right (again) - Zane was a traitor. But, instead of Zarkon giving him what was promised for his services, he has him hauled off. In the meantime, the horrible generator is activated. All seems lost. The Lions and the mines are swept into the generator's whirlwind. The Lions kick in their stabilizers and are able to form Voltron. Somehow, they end up outside the whirlwind when this happens, and bring out the blazing sword. He destroys the generator, which ticks off Haggar. She launches a robeast which Voltron takes care of.
But, it may all be for naught for Lotor still launches his missiles at the Castle. Apparently he forgot that the castle can fly, which it does to escape. Some dead trees and melted rocks was all Lotor accomplished. Voltron caps off the ep by taking out Lotor's command ship (he escapes, of course.) and somehow the force knew Zane was a traitor after all. But they're ok with being repeatedly stupid as far as trusting people cuz that's just what the good guys do...or something.