This is one of several quests given by Sergius Mordanticus in North Freeport. Asking him about what the Freeport Militia does may result in this quest.
You must head to North Freeport and bully Courtesan Fania Falx in to forking over some bribe money. Be stern and she'll give it up.
Return to Sergius Mordanticus for coin and experience.