Earth's champion meets the galaxy's toughest 'Cats in a special by Judd Winick, Al? Garza and Trevor Scott! While attempting to stop Mumm-Ra's mutants from retrieving another Eye of Thundera from an alternate dimension, the ThunderCats are hurled into Metropolis! Can the Man of Steel withstand a blow from the most powerful sword in the universe?
The story opens on Thundera... Mumm-Ra begins to use the recently discovered orbs of Barrack, which allow one to go to anywhere on Thundera, to infiltrate the ThunderCats lair.
As he prepares to do so, a bald woman, Lantana Lin, appears before Mumm-Ra, telling him that he can use to orbs to secure a second Eye of Thundera in another dimension in the city of Metropolis.
Nupil, one of the beasts Mumm-Ra once used as a slave spies on the meeting and tells the ThunderCats, who decide to ride out at dawn and stop Mumm-Ra.
In Metropolis, Clark Kent and Lois Lane attend a tour of a Museum for the Daily Planet. Clark sees the Eye of Thundera and is interested.
As the Mutants prepare to enter the dimensional gateway, the ThunderCats attack. Lion-O slams into the dimensional gateway with the Sword of Omens, but somehow the Mutants manage to get through, pulling the ThunderCats along.
On the streets of Metropolis, Lion-O appears in front of a child playing with a ThunderCat/Masters of the Universe hybrid toy figurine. The child is saying, "Thunder, thunder, thunder-" when Lion-O appears. The people react with fear towards the ThunderCats, because they cannot understand their language. The Mutants, invisible by virtue of kryptonite necklaces they wear, attempt to escape. However the Thundercats can still see them and they attempt to give chase, the police arrive to deal with the ThunderCats.
Cheetara attacks Monkian, and Monkian dodges, causing her to take a car apart. Superman stops her, thinking she was attacking the car.
Lion-O, seeing Superman grab Cheetara, attacks, slashing Superman in the chest. Superman falls back in pain, his suit torn in the chest, realizing that Lion-O's sword is magic-based. Superman feels like he's been hit with Kryptonite.
Superman takes out Panthro with one punch, throws Lion-O into the ground, and tosses Tygra into a nearby building. The ThunderKittens attack and Superman tosses them aside with ease.
Snarf uses the Clarifying Staff of Knowledge to translate their language, and the battling heroes realize what is happening and stop fighting.
Meanwhile, the Mutants head for the Eye of Thundera. Vultureman grabs it, but the ThunderCats and Superman arrive to take it back. The ThunderCats take the Kryptonite amulets and Superman takes back the Eye of Thundera.
Mumm-Ra, now upset, transforms into his Ever-Living form and attacks Superman. Superman fends him off, but Mumm-Ra starts to get the upper hand. Lion-O and the Thundercats step in and take him down, along with the Mutants. Lion-O sends them back into the gateway, which is now re-opened, and the Thundercats follow.
Superman explains what has happened to Lois, and Mumm-Ra arrives home to find that the orbs have been stolen by Lantana, who reveals herself to by Mxyzptlk before disappearing.
Superman goes with Lois to the Fortress of Solitude and places the second Eye of Thundera safely in a display case.