The Legion subject Superboy to a medical treatment that is really a "hypno-block" that prevents him from retaining information about an extended life serum and from wondering why his teammates age so slowly.
Story 1: The Legion's Super-Secret
Brainiac 5 puts Superboy through a hypnotic brainwashing so he could forget something vital, but an emergency arises, causing the brainwashing to be incomplete. They rush to find a group of Sklarians trying to invade the Institute of Life and stealing something vital, but they are rebuffed and sent into the custody of the Science Police. During the mission, Superboy gets the nagging feeling that the Legionnaires are keeping some information from him. When the Sklarians try to steal more experimental equipment, Superboy believes he learns the reason why his fellow teammates are brainwashing him to forget. The truth is that scientists in the future created a serum that could extend life for centuries and the Legion doesn't want Superboy to alter the past by divulging any kind of information about it.
Story 2: Trial Of The Legion Five
Five members of the Legion of Super-Heroes are accused of murder, but are found innocent after all the proceedings of their trial.