You break into the lodge and find a desk on the other end of it. You head over there and open the drawer. In the drawer sits three keys
You examine the keys. That seems to be all that there is in here.
One of these must unlock wherever Amius and Nabi are captured. Let's take one and head back.
The two of you head out of the lodge and walk to the boat.
You go. I will stay here. I want to spy on anything else that goes here. And if you ever need another key, come back and I can swap you one. Now go, hurry.
Select one of the keys and attempt to use it to unlock a lock in another area.