1. The Betrayer from Beyond!
A new group of super-powered teenagers come to the Legion of Super-Heroes headquarters to join the Legion. While most of the applicants are rejected, one makes it through the premilinary trial: Molecular Master. Meanwhile, the energy form of ERG-1, a superhero who sacrificed himself in the line of duty, wanders the Legionnaires headquarters to find a way to get into his special containment suit and come back to life. ERG-1 inadvertently discovers that Molecular Master is actually a robot created to steal a machine from the Legion's headquarters and he finds a way to get into his containment suit, save the Legionnaires and stop Molecular Master from accomplishing his goal. In the end, he joins the Legion of Super-Heroes.
2. The Silent Death
Both stories reprinted in Legion of Super-Heroes Archive #10