The League of Super Villains attacked Metropolis thinking that only Superman and Supergirl were there to defend the city. Superman found out about the planned attack and smuggled in reinforcements. Lex Luthor was leading the attack. He had developed kryptonite gas to use on Superman and Supergirl. He thought that if he could eliminate them, the city was his. During the battle Luthor encountered Supergirl. When he announced that he had kryptonite gas Mary Marvel put herself in front of Supergirl to try to protect her. Luthor hit Supergirl with a gas canister. It bounced off Supergirl's chest. The gas leaked out immediately and Supergirl fell to the ground coughing in great pain. Mary fought with Luthor. Power Girl was nearby fighting Bizarro. He taunted her by calling her Boobie Girl. PG enjoyed felling Bizarro. PG saw Mary fighting with Luthor and helped take him out. After Luthor and Bizarro were bound they were added to their cache of prisoners. Power Girl asked Mary and Atlee to watch their prisoners. PG picked up Supergirl and carried her to a first aid station. Supergirl was showered off to remove kryptonite residue. Supergirl was wrapped in a towel and put to bed. She was given oxygen and PG comforted her until she was able to sleep. Supergirl's recuperative powers were very strong. In a few hours she went home. Luthor had plenty of time to think about his kryptonite gas. Its effects on Supergirl were kept a secret. About a week later Supergirl visited Luthor in jail. Luthor said "I see you survived!" She said to him "Never underestimate me!" Luthor said "There's always next time!"