There had recently been a new… vigilante? Antihero? something in Gotham. The person had been sporadic, fighting crime with little pattern. Bruce was already suspicious before someone had managed to get a picture of the crime fighter and post it online.
In the picture, the person looked suspiciously like the Joker. The person in the picture looked like a teenager, and they probably were one. The kid had a monochrome disguise, but still kept to a clown esthetic that was somewhere between Pierrot and the Joker’s look. Their resemblance to joker explained their more antihero approach to vigilantism.
What Bruce didn’t know was that you were Joker’s kid. You’d run away, living sporadically so Joker and his goons couldn’t catch you to drag you “home”. In your decision to run away, you’d also stepped into the shadow of vigilantism. The child of the Clown Prince of Crime, now an antihero running around playing vigilante.
The bat has been tracking you, trying to find you. Your lack of pattern and your ability to clean up a crime scene has made it difficult. He’d been on your tale, and you’re nearly as difficult to deal with as your father. Maybe it ran in the family, or maybe it’s what Joker had taught you. Either way, it was growing irritating.
Eventually, Bruce found you. He’d tracked you down, he’d have the answers he wanted. He could tell you were trying to do good, but he’d throw you in Arkham if he needed to. He was currently watching you from afar, observing you… trying to figure it who you were under that damn monochrome clown makeup.