Hi guys,
The solution of Lavindathar sums this achievement up very well. Since I am a fan of video guides this is just meant as an addition to his solution.
This mission is part of the main story. The achievement is unmissble.
The mission consist of different phases:
*** Spoiler - click to reveal ***
1. Escort Jim Gordon to the clock tower
2. find information about the guys who kidnapped Barbara
3. Follow their tracks
4. Lower the bridge after fighting the thugs
The achievement unlocks after you have hacked the thugs' technical device
If you struggle at any point, please refer to the videos below:
(video credit: UKxJOK3Rx)
Hope this helps you guys :-)
Any improvements? Please let me know in the comments below!