A group of rejected applicants band together as the Legion of Substitute Heroes and thwart the Plant Men's scheme to take over the Earth.; The Legion recruits Element Lad, who is the last survivor of Trom, to fight the space pirate Roxxas, who killed the rest of the Trommians. He wants to keep his super-power to transform elements a secret, so he joins as Mystery Lad.; Following the death of Lightning Lad, the LSH recruits new member Legionnaire Lemon, or Marvel Lad, who turns out to be Mon-El, finally cured of his weakness to lead and able to leave the Phantom Zone to join the Legion full-time.; Lightning Lad's sister impersonates her dead brother and later joins the Legion as Lightning Lass.; Legion of Super-Heroes reject Jungle King tries to get revenge with his super-beasts.; The Legion of Super-Heroes fight Mask Man, who begins killing them one by one.; The Substitute Legion battle alien impostors from the planet Zyzan who have imprisoned the real Legion.; Jimmy is taken by The Collector to the world Gion-El, which is seemingly inhabited by duplicates of him in the forms into which he has been transformed in the past. But when Jimmy realizes he is being hoaxed, the Legionnaires reveal that he has passed his initiation test and they bring him to the 30th century to officially be made an honorary member of the Legion of Super-Heroes.; Jungle King and his super-beasts are defeated by the Legion.; Mask Man continues to kill the Legionnaires, until he is revealed as a 30th Century descendant of Mr. Mxyzptlk. Superboy defeats him, and the dead Legionnaires are restored as all the effects of his magic are undone.; The Legionnaires are angry and rude every time the Substitute Legion tries to help.; The Legionnaires try to find a way to revive Lightning Lad.; The girl Legionnaires are struck by a mysterious Crimson Virus. Satan Girl tries to take their place, but attacks the girls when rejected. Supergirl follows.; Satan Girl is defeated by the Super-Pets and revealed to be an evil Red Kryptonite duplicate of Supergirl.; Proty sacrifices his life to revive Lightning Lad.