You will be informed of the possibility to approach this mission while roaming the streets of Arkham City #1. It will be possible only after getting rid of Penguin (Defeat Penguin), as the mission is connected with saving the officers who have been held captive by the madman. In accordance with the received instructions, head to the Museum #2.
Don't choose the main Museum entrance, instead start off by examining the northern wall of the building. There you should come across a couple inmates trying to break in #1. It of course would be good to attack them by surprise. During the fight itself, make sure no one is able to pick up a shield from the ground #2.
After the fight, approach the door #1 and press A to knock on it. You will be able to get inside, automatically moving to the Iceberg Lounge. Here, talk with Officer Jones, from whom you will receive a new gadget, the mine detonator #2.