Cossack enters the picture and is enlisted to help Haggar capture the planet and get the Lazon. Cossack begins the task by rounding up some slaves - you didn't think he and Haggar were going to do all the heavy lifting, did you?
He seems to enjoy needling a particular human slave, Joran, who apparently was a former soldier. The other slaves appear to have no pity for Joran, accusing him of once being one of them.
Fun time for Cossack is cut short when Lotor shows up unexpectedly and takes command of the mission (the joking around about Cossack's origins in a toad pond is rather amusing). So off Lotor goes with the slaves to build that new Lazon factory.
More backstory on Joran is learned as some other slaves show their disgust for his willingness in the past to serve under Zarkon when he took over his planet rather than fight back. Joran maintains he simply followed orders.
Meanwhile, the Lions happen to be cruising space and pick up on the Doom fleet. Keith tracks the slave ships to a lifeless desert planet in the Azure quadrant called Zall. Though, he explains, a legend abounds about a colony of people that live underground on Zall but it is largely unproven.
As Lotor drives the slaves to work harder on the base, someone does emerge from the lower depths of the planet and spies on the activity with binoculars. Meanwhile, two slaves who are stilled pissed at Joran for his past try to jump him. During the struggle, Joran falls off the edge of the cliff and falls far below to the desert floor.
Before the Doom robots can gather him up, the mysterious masked and caped spy covers him, then carries him off to his/her underground society. When he awakes, his rescuer reveals herself to be a woman by the name of Omnia.
The Lions approach the planet and get a strange signal instructing them to land at a specific spot. They're suspicious, but investigate. Below ground, Joran gets a tour of the impressive city. Omnia explains that a race called the Darrians built the place but disappeared and that her people - humans, basically - have taken it over. Her kind were refugees from Zarkon, and found the underground city perfect cover to hide from him.
In Omnia's flashback of what happened to her world, we get to see a young, brown haired Lotor on his first conquest. Amusing! Joran then begins to throw himself quite a pity party of his own.
The Voltron Force lands in the underground base and meet Omnia. She begins to tell them about Joran and the base Lotor is building when he makes some odd remarks. He gives them a little info about the base but when they really start to plan an inside stealth job and press for more info, it's too much for Joran. He refuses to help because of guilt over his past sins, which he reveals to the team. Though they're unfazed by his revelations, he still refuses to help.
Joran goes so far as to say he doesn't care if they succeed or fail in their mission, so full of self-loathing is he. It seems Omnia is going to shoot him for such harsh words, but it turns out she meant to save his life - from a scorpion that was nearby. After saving him and giving a mooshy speech, Joran decides to stay and help Omnia and the Voltron Force thwart the Doomites.
With Joran's help, the team infiltrates the base and begins to place bombs at the heart of it. Meanwhile Joran tries to warn the slaves that the place is about to go boom but they won't believe him. That is, until the place starts to blow.
Joran manages to save the two slaves that tried to jump him ealier, and black lion arrives to save him just in time. The Doomies aren't too happy about their base getting blown up, but Haggar managed to make one Lazon powered robeast to unleash upon the VF. Sadly, this robeast is no match for Voltron and is embarrassingly easy to dispatch.
The Doomies head off in defeat while the good guys enjoy being free and victorious. Typical ending!