On Planet Pollux, Bandor and Romelle are welcoming Sven when they get word that their people are under attack by Commander Cossack. Sven and Bandor go off to fight, while Romelle contacts the Voltron Force. Cossack leaves shortly after Sven and Bandor arrive. On their way to Pollux, Allura inexplicably starts getting sleepy and crashes the Blue Lion. She is soon captured by Lotor. The rest of the team looks for her, and gets caught by a Ro-Beast. Now it is up to Allura to get herself out of trouble, and save the day.

Haggar is preparing a new Ro-Beast made from moonstone, which she hopes will make it stronger than Voltron. Meanwhile, on Planet Arus, the Galaxy Alliance has sent a general to be the new supervisor for the Voltron Force. The general doesn't like the team, and thinks they are too inexperienced. He also thinks they rely on Voltron too much. Haggar launches the new Ro-Beast, and the Voltron Force goes off to fight it. The general decides to guide the attack, but his orders end up backfiring on the team causing them to get further into trouble. Space Marshall Graham request Keith to be put back in command. The general learns from his error and apologies to the Voltron Force for misjudging them and is impress with their service to the Galaxy Alliance

Haggar sends a Ro-Beast disguised a harmless, stray cat to Planet Arus. After having the mice trick him out of his snacks, Pidge decides to use the cat to help catch the mice. After being caught, Papa Mouse promises that his children will stop swiping food if they let them go. Later that night, the cat turns into a saber-toothed tiger. The tiger lets Haggar's blue cat into the castle, and they proceed to wreck the control room. The cats also capture Cheddar, and escape. The Voltron Force follows after them in hope of saving their little friend.

What seems like another peaceful day on Planet Arus is interrupted by another Ro-Beast attack. The Voltron Force race to the scene to protect the people. The monster traps Pidge and Hunk in its claws, releases some kind of foam that traps Keith and Lance, and knocks Allura out of the sky. The top of the Ro-Beast splits open revealing a second Ro-Beast, which goes to attack the Castle of Lions, leaving only a shell behind. The Ro-Beast invades the castle and traps Nanny and Coran in the control room. Allura gets the Blue Lion working again, and rushes back to the castle to rescue them.

Lotor, Cossack, and Haggar invade Planet Zal in order to mine its supply of lazon, which is an ingredient they believe will make their Ro-Beasts stronger. Joran, a former soldier for Zarkon and now a slave, gets into a fight with other slaves over his being a traitor. He falls over a cliff, but is saved by Omnia, the leader of the people of Zal, who has been hiding underground. The Voltron Force arrives, and they convince Joran to help them sneak into the lazon factory. Keith and the guys plant explosives, while it is up to Joran to convince the other slaves to get out before everything blows sky high.

In her lab, Haggar and Lotor take a slave and combine his molecules with that of a fish. She then flies with Cossack to Planet Mira, but the fish-man escapes with the help of a jungle woman. Meanwhile, a ship from the Galaxy Alliance, carrying a group of young pilots crash lands on Mira. The pilots are captured by Cossack, but the jungle woman manages to get an injured lieutenant to safety. The Alliance learns of the crash and summons the Voltron Force to come to the rescue.

On the way home from their latest mission, Hunk spots a planet that is home to some friends of his. He had met these kids on one of his first missions right out of the Space Explorer Academy. Hunk decides to take a vacation and visit them. Haggar and Cossack see a golden opportunity to isolate the Yellow Lion. They arrive on the planet and take the kids hostage. Cossack gives Hunk and ultimatum: Hand over the key to the Yellow Lion, or the kids have had it!

A spaceship crash lands on Planet Pollux appearing to be filled with slaves trying to escape from Planet Doom. Sven and Bandor take them back to the castle for medical treatment. Romelle encounters one patient wearing a mask. She tries to get him to remove it, but he refuses. Bandor tells Sven that his house is on fire. Sven rushes home to find Witch Haggar waiting for him. He also discovers that the masked man and the other slaves were actually sent by Prince Lotor, and have taken the castle hostage. Haggar plans to use Sven to set a trap for the Voltron Force.

The Voltron Force meet Mary Ann, who Coran said was the greatest robotics scientist in the universe. Zarkon's forces have taken one of her robots and turned it into a weapon for evil. Mary Ann, who is a pacifist, gets into an argument with the team over whether or not violence is ever the answer. As she heads for her home planet, Caspia, Keith and the others fear she may be walking into trouble, and decide to follow her. Their suspicions turn out to be right as Haggar and Cossack are waiting. Pidge finds Mary Ann first and provides her with cover fire so she can get away. Haggar then captures Pidge and wants to exchange him for Mary Ann and her robotics knowledge.

The Galaxy Alliance contacts the Voltron Force when it learns that one of its members, Planet Oron, intends to leave. Oron has a new leader, General Kruger, who has built up a stockpile of weapons and therefore doesn't see the need for the Alliance or Voltron. The Voltron Force arrives on Oron to meet with Senator Roland, who wants his planet to stay in the Alliance. Kruger has ordered Roland's arrest, and announces that he has formed an alliance with Planet Doom. After a brief skirmish, Kruger orders the Voltron Force to leave. As soon as they're gone, Cossack takes over Oron, and makes everyone slaves. Roland and some rebels sneak into a radio room, and beg Voltron to please come back.

Zarkon has formed a new alliance with Largo, leader of the Rogue Galaxy, and they have started taking over the universe. An emergency meeting of the Galaxy Alliance is called. During the meeting, there is an attack, and the Voltron Force heads out to join the fight. Coran and the other leaders are captured by Lotor, Haggar, and Cossack. Sven manages to slip away. Lotor parades the leaders outside and gives the Voltron Force an ultimatum, turn themselves in or else. As Keith is coming out of the Black Lion, he sees Sven and some guards on the rooftop. They open fire, and during the confusion all five lions take off, but they get a call from Allura that she's still on the ground. So they ask the question, who's flyin' the Blue Lion? As it turns out to be Sven himself

Zarkon enlists the aide of Stride, a legendary Tiger fighter, in his battle against Voltron. Stride wants no part of Zarkon's personal grudges, so Zarkon falsely claims that Planet Arus has challenged Stride's honor. As Stride leaves to fight Voltron, Zarkon welcomes a new ally, Queen Merla. After hearing of Zarkon's plan, Merla decides to head to the battle sight, because she doesn't want Zarkon getting all the credit. Stride meets Keith in a one-on-one fight. Keith earns Stride's respect by fighting valiantly, which leads to Merla attacking both of them.

Merla uses her telepathic powers to make Zarkon place her in charge of the next mission to attack Planet Arus. Meanwhile on Arus, word has been spreading that King Alfor is preparing to return from the grave. Some townspeople find a cave that has a statue with a golden shield that is believed to have belonged to Alfor. Allura, wanting to believe that her father has returned, heads for the cave with her teammates right behind her. It turns out to be a trap. The guys get trapped in the cave, and Allura gets taken prisoner by Merla.

Zarkon oversees the wedding of Lotor and Merla. He sees the wedding as the way to unite their two evil kingdoms. Meanwhile on Planet Arus, a young woman named Taryn pines away for her lost love, Ro, who was taken as a slave to Planet Doom. Ro shows up with two mystery women, Merla and Haggar in disguise. Merla claims to have a crush on Keith, and in exchange for bringing Ro home, she wants Taryn to deliver a jar of fresh honey to the castle as a present for his birthday. Taryn gives the jar to Allura, who ponders her own feelings for Keith. After Taryn returns, Ro reveals that the jar actually contains poison. Now they have to get to the castle and warn the Voltron Force before any of them drink it.

Haggar tries to send a baby Ro-beast after Queen Merla, but Merla's pet buzzard catches it. Haggar apologizes, and offers to help Merla conquer Arus. Meanwhile, on Arus, there is a parade taking place honoring the planet's leaders. Merla's forces attack. Keith and Allura try to get the villagers to safety, while Lance, Hunk, and Pidge race to get to their lions. In protecting the villagers, Lance, Hunk, and Pidge get zapped with a freeze ray, and their lions are sent over a cliff, and to the bottom of a canyon. After getting the villagers to the castle, Haggar makes her baby Ro-beast turn into a full sized one, and sicks it on the castle. With the other three frozen, Keith and Allura have to face the monster by themselves.

Philos, a half planet and half comet, is getting ready to pass by Planet Arus for the first time in 52 years. Philos has been taken over by Lotor, who has been having the slaves build a monument to Allura. Zarkon tries to have his son arrested for disobeying him, but then Lotor shows him a new weapon to destroy Voltron and conquer Arus with, the Herculean Generator. Meanwhile, Count Zane of Philos arrives on Arus, and informs the Voltron Force that Zarkon now controls Philos, and has the Generator. They also get a distress call from the Galaxy Alliance that one of their ships has crash landed on Philos after a battle with Queen Merla. Zane offers his services, and everyone except Lance is ready to accept his help. Lance thinks that Zane is leading them into a trap.

Lotor tries to attack Zarkon from behind. Zarkon catches him in the act, and orders his arrest. Meanwhile on Arus, a young woman asks the Voltron Force for help for her sick mother. Her mother had come upon Haggar, and the witch responded by casting a spell to make her ill. Allura gets a vision from King Alfor's ghost telling her that the way to break the spell is from a magic cadmium flower. When the flower blooms, Haggar sends her blue cat to steal it. The team follows her to Planet Pollux, where they find out that Zarkon is building a secret military base. When the Ro-Beast attacks, the Voltron Force is aided by an unlikely ally.

Princess Romelle is visiting Allura on the day of King Alfor's Eclipse. While his sister is away, Prince Bandor gets a call from the Galaxy Alliance that Queen Merla has been captured by the Muses of Norn, but they will only turn her over to someone of rank. Bandor confronts the Muses, and their leader turns out to be Haggar in disguise. Lotor also arrives, and destroys Bandor's fleet. The Voltron Force flies to the rescue. Lotor tricks them into chasing him into the sun of Norn. He then escapes through a space warp, and leaves them to fight Haggar's latest creation, a Firebird Ro-Beast.

All over the universe, members of the Galaxy Alliance are rising up and striking back against Zarkon's forces on their planets. The Voltron Force decides that now is the perfect time to strike Planet Doom and stop Zarkon once and for all. Zarkon once to leave in his Doom Ship and face them himself, but Lotor steals the ship and wants to take the glory for himself. Zarkon takes over the ship by remote control and decides to ram it into Voltron. Queen Merla saves both Voltron and Lotor, but in the process Lotor is taken captive. Merla approaches the Voltron Force, and asks for their help in saving Lotor.

After recharging the Lions back on Arus, the Voltron Force heads back to Planet Doom to challenge Zarkon. Merla convinces Lotor to try being good. Merla and Lotor decide to help the Voltron Force. Zarkon's robot troops bring a group of slaves, and threaten to hurt them unless Voltron surrenders. Lotor sees through the deception, and hurls his sword at one of the slaves. The slaves are revealed to be more robot troops in disguise. Lotor leads the Voltron Force to Castle Doom, where they confront Zarkon in the throne room. The Voltron Force is caught in a trap with a Tentacle Bomb. Now they must escape before the entire planet blows sky high.