When talking to the admiral you've been sent to, he tells you that the corsairs have been removed from his custody and placed into house arrest by a rival admiral. He suggests you speak to that rival to find out more.
This sends you to meet yet another contact, giving you a glimpse of the internal politics in the admiralty in the process.
The story line splits after completing this mission. The next set of missions are dependent on the follow-up mission you complete. You will align yourself either with Yusuf in Threatening Posture or Uncle Ibrahim in Cooler Heads Prevail