Keith and the space explorers take the first steps on their journey to revive Voltron. They find the legendary Royal Castle on the surface of Planet Arus. Inside, they meet Princess Allura and the wise Coran. The Princess declares them to be the planet's new guardians. Together, they unravel the mystery of Voltron's disappearance.

Keith, Lance, Sven, Hunk and Pidge ask for help from the Princess Allura to find Voltron. With guidance from the ghost of her father, King Alfor, they find four of the five keys needed to form Voltron. With no choice, they head into battle with only their robot lions to keep back Doom's soldiers.

Keith and the team uncover the key to the Black Lion, just as King Zarkon's Robeast is about to rain havoc on Planet Arus. Together, they are able to form Voltron's most powerful weapon, the Blazing Sword! But the battle leaves Sven uncertain about his role as a member of Voltron Force.

Keith, Sven, Pidge, Hunk and Lance scour the surface of Planet Arus, looking for brave citizens willing to help them fight Zarkon. Scared because of the recent attacks, only Princess Allura herself is willing to join Voltron Force. When King Zarkon's best gladiator is turned into a Robeast by Hagar, not even Voltron can stop it. Only if Allura can find a way to help with Arus be saved.

Yurak's attack fleet is soundly defeated by Voltron. Hagar comes up with an evil plan to get Voltron out of King Zarkon's hair for good. She sneaks up to the Voltron Force while they are giving out food to the troubled people of Arus. Hagar isolates Sven from the others and badly wounds him. Without Sven, Keith and the team must face Zarkon's new Robeast without forming Voltron!