The Alliance calls a meeting at Galaxy Garrison, to which the VF, Coran and Sven also attend. While they're discussing strategies, the Rogue Galaxy commander (who is totally hideous by the way) attacks Earth. It's a lot like the VV ep, Raid on Galaxy Garrison here, and I'm pretty sure it even uses actual footage in spots from that episode. Largo, the aforementioned commander, contacts those in the meeting to gloat and speak of how they're "finished". His demands are surrender or be crushed.
But the VF don't want to give in. Keith thinks the bullies the Rogues are will run when they face them down. That and the Alliance has a new weapon, stingrays. But Lotor makes short work of that and encloses Garrison Island inside some kind of force field.
It takes some time, but the VF finally get to the Lions and launch. In the meantime, Lotor breaks into the meeting in the meantime, and takes everyone hostage including Coran and Sven. But as Cossack makes a speech about how keen of eye they are, Sven slips out. He runs into some trouble with robot guards but Keith shows up in black lion to save his bacon just in time.
The hostages are paraded out as bait, and the VF must decide whether to give up or fight on. Coran gets whipped by Lotor for being a wise ass, and Keith hates it but he knows they must surrender. They all come out of their Lions and it looks like it's over. Lotor can't wait to claim Allura as his bride.
But first, he and Cossack ride over to the black lion to personally cajole Keith as he is the last one out of his Lion. But Keith notices Sven on the roof above the balcony with a group of armed Alliance guys and doesn't allow himself to be captured. Sven opens fire on Lotor. While this is going on, everyone escapes and the team gets back in the Lions...except the Princess. But then...who's flyin' blue lion? You guessed it. Sven!
The Lions fight with Zarkon's ships for a while until the Princess lets them know she got away from Lotor and that he's turned tail and run. It looks like the raid is over...except Haggar has a parting gift for them in the form of an insect-like robeast. The team forms Voltron immediately. After a long battle where Voltron almost gets toasted by voltage, he turns the table on the robeast and finishes it off. Seeing Voltron defeat the Rogues, the other leaders and inspired to unite and fight. Together, the menace is turned back.