This formally ends the Fort Forthinry storyline and sends you in search of the wounded dragon, Vorkath. For those up to date, Vorkath was wounded in the Zemouregal & Vorkath boss encounter during Battle of Forthinry, after Zamouregal raised the dragon from the dead. After facing both of them at the fort, Vorkath flies away.
This quest will take you to the frozen island of Ungael, and if you can brave the cold and explore, you may be able to solve some mysteries and uncover secrets the island offers.
Continue on and explore and somewhere in the Frozen Cliffs there is a brand new necromancy Ritual site that you can use.
There are more rewards and mysteries to unlock, and also a dragon to find.