A storm caused the PCs' vessel to sink and is now forcing them to seek shelter in the keep on the remote isle. Their goal is to locate a boat or some other means of transportation to return to the mainland after the storm has passed. But first, they must survive the tests and traps the island's inhabitants have set for them.
Chris Perkins is the author of this adventure, under a pen name. Check Dungeon Magazine issue 58, page 60 for confirmation of this.