The Joker has trusted T.O. Morrow to perform experiments to test and improve the effectiveness of his Joker Toxin. However to the Joker's surprise, Morrow betrays him, using Ace Chemicals as his hideout, with an army of his creations mixed with the toxin. He has even managed to reform Chemo, so you and your group must help Batman/Joker to take Chemo down and defeat Morrow.