Worldwide, people and objects suddenly start "falling" upward into the sky; events are linked to a force from a distant, newly discovered planet. Underdog flies there to investigate and encounters the Magnet Men; who demand all of Earth's iron within 24 hours else they will pull Earth away from the sun by means of a super 'gravity gun'. The deadline passes and the Magnet Men carry out their threat; Earth freezes over and everyone panics; to save Earth, Underdog flies back to Magnet Planet to do battle...