The Crystal Queen

Lion-O has to brave an ice palace to rescue an endangered bird from the clutches of a cruel and greedy queen.

While driving through the forest in the ThunderTank one night, Lion-O and Panthro see a glowing object streaking through the night sky. They try to keep pace with it but the tank stop abruptly. Upon inspection, Panthro finds that the Thundrillium module on the tank ran down, even though Snarf was supposed to recharge it. Panthro heads off to the Cats Lair to fetch a spare module, leaving Lion-O to guard the tank.

Panthro reaches Cats Lair shortly, where Snarf is serving dinner to the rest of the ThunderCats, and asks him about the spare module. Snarf can't find it at first but eventually remembers where he kept it. As Panthro is leaving, Snarf asks to join him but Panthro refuses, saying that there is no need as he will return with Lion-O very soon. However, Snarf gets a bad feeling that Lion-O is in danger and sneaks out after Panthro.

Meanwhile, Lion-O hears strange music coming from the nearby Berbil Village and heads off to investigate. Upon reaching, he sees the source of the music is a beautiful bird, who Ro-Bear-Bill tells him is the rare Arrietta Bird. The birds singing ripens the Berbils' fruits and ensures that they will get a good harvest.

Suddenly, the streaking object that Lion-O had seen earlier returns and it turns out to be a rocket powered sleigh. Ro-Bear Bill explains to Lion-O that the occupant of the strange flying vehicle is Queen Tartara of the Crystal Kingdom and she is always trying to steal the Arietta Bird so that it may sing for her alone. As the vehicle makes a second pass, one of the drivers manages to nab the bird. Lion-O springs into action and grabs onto one of the runners of the sleigh as it flies off to the Crystal Kingdom.

When Panthro arrives back at the tank and does not see Lion-O, he goes to the Berbil Village where Ro-Bear Bill explains all that had happened. Panthro then gets in the tank and drives off towards the Crystal Kingdom but is unaware that Snarf had stowed away in the tank. Half way up the mountain, Panthro comes to a fork in the road and as he gets out of the tank to investigate, he hears Snarf and discovers the stowaway. He then tells Snarf to wait there as he checks out the two paths. Snarf however, notices Lion-O's footprints in the snow and races off following the trail.

Lion-O who had fallen from the flying sleigh near the Crystal Kingdom, sneaks into the palace by disguising himself as one of the guards. He makes his way into Queen Tartara's treasure room where the Arietta Bird is being held but before he can do anything, he is discovered by the queen who encases him in a giant crystal.

Snarf follows Lion-O's footprints all the way to the Crystal Kingdom and then burrows under its walls. He surfaces in the treasure room and uses the Arietta Bird's high pitched voice to break the crystal encasing Lion-O who immediately summons the ThunderCats. Panthro arrives in the ThunderTank, breaking through the wall of the palace. Lion-O and Snarf hop in the tank and the trio drive out destroying another wall. This causes the entire palace to start collapsing and the Arietta Bird escapes by flying out through a hole in the roof.