Much of the plot must be discussed as i only have the big idea, no details.
 Everything starts when a group of horker hunters get lost in the Sea of Ghosts after a storm, their ship ends up in a strange island that does not appear in any map, the hunters managed to return to Skyrim with news about this island, soon all the Jarls found out about this and the High King decided to call them all for a meeting. They decided to explore the island with the help of mercenaries so they would not lose good soldiers in case the island was dangerous.
So your character is one of those mercenaries or settlers who is sent to the island, what will they find? who knows? get your sword ready just in case.