Years ago, the Voltron Force ultimately defeated Prince Lotor, resulting in his horrible disfigurement and Voltron being retired. But before Lotor was captured, he sent Castle Doom away to an unknown location. Now in the present, Keith, Allura, Amalgamus and a supposedly reformed King Zarkon are trying to learn from Lotor where Castle Doom went. Meanwhile, space pirates have reemerged and begun attacking Alliance ships and colonies.
Lance strike out on his own in Red Lion to hunt down the escaped Lotor. Space pirates, Queequeg and Lafitte, lead him into a trap set up by Lotor. Against orders, the rest of the Voltron Force take their Lions to rescue him.
Lotor holds a phony peace summit with Zarkon and Keith, with Lance secretly coming along. Lotor uses a crystal Haggar gave him to enter the Dream Dimension. Lance pursues and finds Haggar has been looking after Castle Doom all this time.
Amalgamus suspends the Voltron Force and replaces them with robot pilots. The robots first test is to protect Outpost Opal from Lotor, but it becomes clear only the original pilots can achieve victory.
The Voltron Force are given a false order to attack Planet Geo and are forced to repair the damage they did to a mining colony, where they encounter some mutated space lice. It's all part of Lotor's scheme to attack the Castle of Lions.
Haggar casts a spell on Hunk, turning him against the rest of the Voltron Force. The spell also turns Yellow Lion into a destructive Gray Lion. The rest of the team have to find a way to save Hunk and rescue Amalgamus from Lotor.
Lotor kidnaps Judge Armistice, whose signature is needed for a peace treaty. Haggar then uses her magic to make Lotor look like his old self. All he needs now is to get Allura to Castle Doom to make her his bride.
Radiation may have made Planet Geo uninhabitable, but it's made it the perfect breeding ground for Lotor's giant shonga, Dominus. As Lotor lets it loose on the Alliance, the Voltron Force has to defeat this living creature without destroying it.
Lotor has Haggar summons five robot dragons, which can form the powerful Dracotron, to destroy the Voltron Force. But Lotor and Haggar soon lose control and must have a brief alliance with the Voltron Force to defeat Dracotron.
Keith discovers Zarkon is only pretending to be reformed. Before Keith can warn the others, Haggar casts a spell that turns him into a feral beast and makes him forget what he knew. While they don't know what caused it, the rest of the Voltron Force try everything to find a cure.
Pidge is sent to planet Glacia to get Thunder-Ice, a new discovery that can stop Nova-99 from destroying a solar system. Zarkon manages to get Amalgamus to send a cyborg named I.G.O.R. with Pidge. Not surprisingly, I.G.O.R. turns on Pidge and tries to destroy him and Green Lion.
Haggar seeks to avenge the break up of her relationship with King Alfor. She imprisons Alfor's spirit in a Crystal Robeast, which soon does battle with the Voltron Force. But if they destroy the robeast, they will also destroy Alfor's spirit.
Keith and Lance sneak into Castle Doom and try to get proof of Zarkon's duplicity.
The Voltron Force are accused of rebellion against the Alliance. Coran defends them in the trial, while Amalgamous prosecutes.
To save the large populations of the Troika Moons, Allura must consider sacrificing the robot lions. Lance disagrees with what she decides and quits the team.
Alliance reporter, Ueep Ueep Cheromoya, interviews Amalagamous about each member of the Voltron Force. Meanwhile, Lotor plots to pull the plug on Galactic Action News.
Keith, Hunk and Pidge try to stop Zarkon from attacking Galaxy Garrison, but they have to rush off to save Lance. Meanwhile on Arus, Allura meets the spirit of Ariella, the first queen of Arus, and begins learning more about Arus and the robot lions.
With Lance saved, the Voltron Force are heading back to Arus. They have to stop Zarkon, however with their robot lions destroyed, they're at a great disadvantage. But Queen Ariella reveals to them a way to bring the lions back.
While trying to take back Yellow Lion's lair from Black Draco, the Voltron Force learn of an alternate dimension where Voltron can be reconfigured into a powerful new form.
Zarkon invokes an ancient Arusian law, which allows him to challenge the best fighter to a battle. Lance and Lotor are selected to fight.
The shonga Dominus is back and Allura tries to make a home for him in the Castle. But it becomes obvious Dominus needs to go back to his actual home, the Stealth dimension. Joining forces with Kolak, Haggar and Lotor try to get Dominus back on their side.
While in another dimension, the Voltron Force encounter Kolak the Hunter, who is of the same race responsible for Dracotron. Kolak plans to use his Stealth technology to make the Voltron Force biomechanical beings like himself and only Pidge can save them.
Lance and Lotor get sucked into Claw Mountain. They arrive in a parallel universe where Lotor commands Voltron and the Castle of Lions, while the Voltron Force are considered rebels.
Allura learns special mind skills can allow the Voltron Force to control the lions without having to be in the cockpit. Pidge is unwilling to try this, though, since he was an outcast on a planet of telepathes. But the Voltron Force might lose to Zarkon in battle, if Pidge doesn't try.
The Voltron Force and Coran deal with space pirates to rescue Amalgamus. Once Amalgamus is saved and repaired, the Voltron Force attack Galaxy Garrison to force out Zarkon, Lotor and Haggar.
The Voltron Force are tricked into entering a replica of Castle Doom, where Haggar makes their nightmares become real.