Batman: Gotham Knights

You follow the reports and it seems that all of the recent victims of Scarecrow's fear toxin all have something in common. They seem to be workers at the Wayne Corp. Chemical Labs. Obviously, he's going to want some chemicals, but for what purpose you can't speculate on yet.

You drive down to the Chemical Labs and break in through the back. The Scarecrow is standing in the middle of an empty room, dumping chemicals into a straw sack and laughing and singing about something. Sometimes, he'll stop and talk to no one in particular.

He's clearly insane, and you need to stop him before he can unleash whatever it is he's scheming.