Head out of the small room the doctor was in and turn left. Cross the center of the room and you should see a shutter door with a motor above it (it will be gold in detective mode). Take out your new toy which is right on the directional pad and then hit RB/R1 to shoot an electric charge. Note that in some cases you want to hit RT/R2 instead to have the opposite effect (in this case, it would close the door instead of open it). Go into the small room and do the same thing above the next door which will reveal a door right behind it. This one you just walk through with the A button. Grapple up to the ledge and enter the air duct.
Pop the vent open and drop down behind these guys. You can do a silent takedown or practice using the guns quickfire stun attack. It really does just stun them and is nowhere near permanant so keep that in mind. This guys really are nothing though and there are only four of them so take them down however you please. Once done, you should find yourself in a familiar room. Just turn around and find the door. Keep heading backwards through doors until you are back in the loading bay area from before and Harley Quinn will talk to you through the giant Joker Mouth on the wall.
