You should now be back in control of Batman, so grapple up to the highest possible point. Your marker will lead you to the GCPD, so glide your way to the police. As you get closer to the department you should be able to spot the men patrolling the front. Since they are all armed, you will need to take them out one by one. Do not try & fight them head on.
With the entrance cleared out, you will hear a phone ring. This is connected to a side mission. So you can ignore it as your real objective is the generator over the shutter door. Charge the generator to allow for a gap that you can slide under. Inside of the building will be a set of doors & console nearby. Hack the console to gain access to the Penguin’s radio frequency. Once you are patched in, enter the doors.
Gotham Police Department
You need to grapple up into the ceiling & then head forward into the ventilation. Make your way through the small space to encounter the first difficult predator section. There will be five enemies total to focus on.
Begin the section by eliminating the thug near the front, & follow that up by taking down the second thug facing the adjacent door. You can now head back up into the ceiling, & stalk the two thugs on the outer edge of the room. With the third & fourth thugs removed, you can defeat the final thug & move onto to the next room.
You will have a short conversation within a cutscene, & told about the Penguin’s hideout in the museum. Make your way back to the entrance & and hack your past the Penguins flimsy attempts to slow you down.