This quest will begin automatically after you have spoken to Brutus Plutocratio at the end of the quest The Escaped Slaves.
Talk to the Slave Hunter with the exclamation mark (!) over his head.
Treachery! The slaves have been freed.
Kill all 8 Slave Hunters when they become hostile to complete the quest and receive your reward. Although Brutus Plutocratio also becomes hostile, you do not need to kill him to complete the quest or receive your reward.