The Cardinal tells you that the pirates in Tortuga are actually running a secure bank. He would like to know more about the men behind it and asks to to go there, open an account, and see what you can find out.
There will be no fighting required for this mission, you will only have to talk to a number of NPCs in Tortuga. First you will have to visit the bartender at The Empty Gibbet tavern who will tell you where to open your account. This will take place in a separate instance near Kidd's dock. After chatting with the girl there, you will only need to get it authorized by talking to Salvador Callar, who in turn will tell you that there's a bank officer aboard your ship who wants to talk to you. Talk to the nearest Coxswain to access this last part of the mission.
However, note that this is the point in the mission which lets you switch your alliance from The Inquisition to the Knights Templar. Specifically, your (ONLY!) chance to do this arrives when talking to Mogens Brisebois. At one point, you will be confronted with two different conversation options: either for the Inquisition ("Well, that makes it easy then. All I have to do is silence you!"), or for the Templars ("All right, you convinced me. What do I have to do?"). The mission chain then branches out depending on your choice at this point.
- Make a Deal with Brisebois