Dr. Byron Meredith is not a nice Doctor... Former Arkham staff turned private-practice specialist for people obsessed with Joker and all around arrogant dick. Well, sucks for him, because his burnt as all hell body was just found dead, ID'd only by dental records. Meanwhile, Batman finds out that all of the League of Smiles were former patients of Merideth, so time to investigate!
So while Batman is investigating Merideth's place, being attacked by one of his former patients, relapsing from the lack of drugs, the League of Smiles arms themselves to the teeth in order to strike more targets by order of the Merrymaker.
After Bruce defeats the circus strong-man reject, he uses a hard drive he found in Meredith's place to find out a whole bunch of things about all the League of Smiles members, as well as notes on each of their files about them being suitable candidates to be controlled or not. Bruce also finds a bunch of info on Merideth himself, finding that he was in deep with many people, ranging from his ex-wife, debtors, etc.
While investigating the League of Smiles further, Bruce intercepts a police report that a bunch of Joker victims have been sent to the morgue. Using the hologram thing (as seen in Batman #2) he installed in the morgue, Bruce scares the shit out of Bullock, and starts going over the corpses with Gordon, immediately determining that it wasn't the work of the Joker (he would know) but made to look as such, pointing out the smiles on the victims. Then it clicks, as Bruce looks at the charred remains of Meredith, it all comes together...
So much so, that Bruce figures out where the League of Smiles will be attacking next, and baits the three members up to where he finds, and punches out the Merrymaker, revealing him to be Dr. Merideth, who manipulated the League of Smiles members into serving him, taking out those who he felt had wronged him, and all under the name of the Joker supposedly.
This doesn't please the League of Smiles, who gets in a few seconds of beating (that Batman allows) before they're all taken in.
Elsewhere, Ogilvy is notified that the police do not believe the kills he committed to be the Joker, but it doesn't matter to him, because the people on the street believing it was Joker, and now they're all flocking to him, the plan is coming together!
Then moving on to the back up, we see how Meredith took inspiration from the Joker. He was a colleague of Harley Quinn while she treated the Joker and noticed how infatuated she became with her. He thought he could use that sense of twisted inspiration the Joker creates to his advantage, and the rest is history. He tries to level with his old psychiatric pal to just recommend him for Blackgate, but his Dr. decides to screw him over, declare him insane, and off to Arkham the Merrymaker goes!
WHATS THIS!? That Doctor is also infatuated with the Joker?! OOOOOooooOOOooooOOOhhhh Spooky!