Pirate Pete, the guy who recruited you for Rum Deal and "teleports" you to Braindeath Island, is among the council members that need saving. For him, you need to make fishcakes, which require breadcrumbs, ground cod, ground kelp, and crab meat. While most of these ingredients are easy to get to, the crab meat isn't. It requires you to go diving and deal with some mogres (marine ogres) who keep a pen full of giant crabs. After you're done with your swimming trip, you can get the cook to look up the recipe for fishcakes, feed one to Pirate Pete, and Aris will teleport him to safety.
Congratulations, subquest complete!
