People are disappearing on Mercury, and the Legion tries to get to the bottom of things.
Story 1: Will The Last One To Leave Mercury Please Close The Door?
The Legion of Super-Heroes rush to the planet Mercury, in a medical center, after receiving a message from Karate Kid that he would be there. Believing that Karate Kid is in a dire predicament, they rush to find Karate Kid with a friend, iris Jacobs, who was recently cured of a malady. The Legion are then asked to stay by a doctor who tells them that staff and patients, at night, have been disappearing, even though the planet is covered in molten lava. They eventually learn that Mercury has native inhabitants known as Thermoids, fire beings. The missing staff and patients were accidentally disintegrated by the Thermoids and it was all a matter of miscomunication.
Story 2: A World For The Winning!
The Fatal Five appear to have turned over a new leaf, but their evil ways eventually are shown as they fight some Legionnaires. Superboy is forced to leave his teammates to gather reinforcement, much to his dismay.