You will be informed of the possibility to approach this mission with a marker on the Arkham City map, pointing an act of violence #1. It will probably point to Park Row, where you began the game. After reaching the spot, you will note a group of thugs attacking an innocent political prisoner #2.
Try to attack the enemies from above if possible and afterwards eliminate the others in direct combat #1. Be careful, as they will be very numerous. Once you're done with them, talk with the saved prisoner who turns out to be Jack Ryder #2.
The further part of this mission is very similar. From time to time you will note a new marker pointing to an act of violence #1 and you will have to eliminate a few thugs after reaching the area. I'd especially recommend looking out for the ones equipped with firearms #2. You should attack them by surprise early on and during the fight itself often evade and throw weapons out of their hands. Keep repeating the above actions until you save all the political prisoners.