The Beast has captured Planet Rock, and starts to round up the planets' population. On the Prison Planet, the fight between the two factions continues, but Graveheart, Cryos, Jade, and Femur are reunited. The Sand people find the Prison Planet and guide the planet back to the Alliance system. The planet teleports back, appearing between the Beast Planet and Planet Rock. As the Beast Planet's claw closes onto the Prison Planet, Sternum activates the teleport engines, teleporting both the Prison and Beast Planets to parts unknown.

The Beast Planet demonstrates its might, launching an armada to attack Fire while training its powerful cannons on the Battle Moons. A stray blast threatens to destroy Ice, but Tekla and Lady Zera discover world engines hidden within the planet, which move it out of the path of the blast.

The Beast Planet targets planet Fire. Graveheart and Tekla must hurry to find the world engines. During the invasion, Graveheart is injured while saving prince Pyrus. The Grand Vizier witnesses the sacrifice and reconsiders his judgment towards the outlanders. In the end, everything is lost for planet Fire but the Grand Vizier sacrifices himself and tells prince Pyrus that his new friends are indeed worthy ones. Prince Pyrus orders the Vizier to evacuate with the rest of his people, because he still needs his guidance and company. The Vizier disobeys, saying that Pyrus is old enough to rule, and that the Vizier does not want to die a coward. The Grand Vizier uses the world engines to ram Planet Fire onto the Beast Planet's claw, hoping that it will destroy the Beast Planet, The Beast Planet consumes planet Fire anyway, killing the Grand Vizier.

Emperor Femur and Pelvus must make good their commitment to return to the Alliance. They agree to feed all the people of the Alliance with the resources of Bone, and so Bone rejoins the Alliance.

Captain Blaze and his renegade squad steal one of the Battle Moons and attempt to regain their lost honor in destroying the Beast Planet. But when Blokk and his battle fleets almost seize Prince Pyrus, Captain Blaze returns to save his young lord. At the command center, Jade is contacted by Lord Mantle to finish their bargain.

The Alliance travels to planet Sand. Lady Zera meets one of the Sand People, Zuma. She is a telepath. In the end, the great Sand People save the day with their mind power.

Jade, princess Tekla, Lady Zera, Pelvus and Zuma head for "Moon Over Mayhem" to socialize. In an attempt to reconcile, Tekla gives Jade the key of the Cluster defenses. During this pleasure trip they are attacked by Fire's pirates and smugglers as well as Lamprey and her drones.

The Alliance of the Cluster find Planet Jungle. They are willing to sacrifice this non-living world to trap the Beast Planet and Blokk's forces. On a trip to planet Jungle they place explosives but living plants ask for their help. Tekla finds out the planet's world engines were destroyed long ago. The vegetation on this world is doomed. A sentient plant asks Femur to preserve a small part of the planet's life. Planet Jungle explodes, but the Beast Planet is unharmed.

The Alliance is surprised when Planet Fire catches up to them. Apparently the Grand Vizier is alive but his personality seems different. It is revealed that it isn't the Grand Vizier but a creation of the Beast planet. The Alliance retreats into a nebula to evade destruction from Blokk and his battle forces.

The Alliance detects a signal from a mysterious planet which is determined to be a battleground. Graveheart and Cryos are traveling together as are Jade and Femur. The two groups crash land separately and lose contact with their fleet. The miner and the Ice King are found by Jewelia and her band of criminals. Jewelia develops a liking for the former rock soldier. Jade and Femur meet Sternum who is a tough warrior from planet Bone. Sternum relocates the prison planet to another location evading the scanners of any possible enemies.

It turns out the prison planet can teleport itself. Sternum is revealed to have been Femur's brother. Tekla and Pyrus must confront Lord Mantle, who wants to rule the Alliance. Mantle shuts down the defenses for the entire Alliance endangering the fleet. Meanwhile, Jewelia and Graveheart lead an attack on Sternum's camp but are driven off by its superior arsenal. Sternum was the rightful ruler of Bone before being overthrown by his brother and seeks revenge on Femur. Graveheart and Jewelia retreat while Tekla has no choice but to pass over leadership to Mantle. The Rock King reveals a key which is the defense key given by Tekla to Jade. On the prison planet Jade is set to kill Femur.

Both factions of the prison planet prepare for their next battle. Blokk and Mantle engage in battle; Blokk proves victorious and kills the Rock Lord.

The episode opens with Lord Mantle's funeral. As Graveheart speaks and the Alliance watches, Blokk kills three Rock soldiers. Tekla, Pyrus and Zera confront Jade to demand why she would betray them, and Graveheart reveals that it was to convince Mantle to lend them the Battle Moons for the fight with Remora. Graveheart then asks Jade to be the next ruler of Rock. Blokk enters the World Engine and kills all the Rock soldiers except the captain. He steers the planet towards the closest star. He then contacts the Alliance and demands that Graveheart face him. Voxx repairs the world engine allowing Jade to steer the planet away as Graveheart finishes Blokk off by plunging the Forcefield Generator inside him. In the aftermath, Jade makes Graveheart an official Rock citizen, and the series ends with the Beast Planet devouring another planet, the subtitle below echoing the first episode: "Planet Reptizar: On Doomsday".