Gamma Monsters are attacking S.H.I.E.L.D. Headquarters and Nick Fury is calling all Avengers to help out in defense the air base from their attacks. Place agents on the same row as the Gamma Monsters so they will begin to shoot them down before they come in contact with the agent. Move your three agents from row to row as needed because the monsters will be attacking from everywhere. When the Avengers come to help they come in a big way and blast away all of the monsters in a single powerful attack. Keep the defenses up until you can make the monsters retreat.