An old iceberg on Hook Mountain begins to melt, releasing an ancient being known as the Ice King who had been trapped in it for a thousand years. He begins to destroy Snowman's castle at the top ofHook Mountain. The Snowman tries to stop him but is frozen solid by the Ice King. Snowmeow, his faithful companion, seeks out Lion-Obut upon his arrival on Hook Mountain, he too is frozen solid by the Ice King. Panthro, Tygra and Snarf arrive in the ThunderTank but they too meet the same fate. Only Cheetara is left and she arrives just in time to place the Sword of Omens in Lion-O's hands, freeing him and he in turn frees the rest of the Cats and the Snowman.After a brief battle with the Ice King, the Cats realize that he is not evil and is just trying to get into the castle to find an ancient egg which has an image of his wife. The ThunderCats help to obtain the egg from the Pterodactyl guarding it and give it to the Ice King. After taking one last look at the image of his queen in the egg, the Ice King melts away.