The Riddler is looking for the answer to the ultimate riddle, the true identity of Batman, so he hatches a plan to capture Batgirl and Robin in order to force Batman into the open to rescue them--and Batman will need some help to preserve his secret.

When a wicked werecat plagues a big cat park on the outskirts of Gotham City, Mystery Inc. joins forces with Batman to crack the case, but little do they know, more than one crafty kitten is at play in the preserve.

Harley Quinn and Poison Ivy escape from Arkham Asylum and head back to Ivy's hideout; however, Harley proves to be a demanding roommate, so Ivy helps her take over a carnival and even grows her plant versions of Batman and Robin to boss around--but when Poison Ivy feels she has done enough and withdraws from the field, Harley discovers that being a criminal boss is a lot more difficult than she imagined.