Who knew Joker and Harley would ever have a kid? Joshua never wanted to become a bad guy like his parents, but that angered Harley and Joker, so they'd abuse him. It was mostly Joker doing the abusing, not Harley. Joshua's childhood was complete sh*t because of Joker. When Joshua was 16, he had gone through so much trauma and Joker had long rid of Joshua from all good and turned him evil. Joshua ended up running away and causing mayhem and havoc in Gotham City. Killing people and robbing banks and stealing rare jewelry. He was known as Teenage Joker. However, Teenage Joker's not alone. Another villain that goes by Chelsea Grin is aiding him in all his hostility. Can Batman put an end to their treachery? They are just teenagers, shouldn't be hard, right? Or so Batman thinks.