Story related, cannot be missed.
You will given the quest entitled "Liberate Captain Marshall" after you finally make contact with Elizabeth and the resistance. She will task you with breaking Captain Marshall out of jail. Again just as with Dead City, be stocked up and ready for a fight, this time with the Authority.
Make your way through the facility and eventually you'll rescue the good Captain. After that you two will venture together and you will have to keep him alive while fighting troops. After an encounter in the courtyard, Marshall will leave you behind to make your own way out of jail. At least he is kind enough to leave behind this achievement as he exits.
A helpful tip for those going for the Gotta Catch Em All achievement. This area (like The Well in Wellspring) cannot be replayed so be sure you pick up the 6 cards here before moving on.