Defeat Summoner Kanthin at Manaforge Duro, on the island to the north of Sunfury Hold, and reclaim the Stone of Glacius from him.
The next thing we must do is reclaim my familiar, Glacius, from the blood elf summoner who holds it captive. Summoner Kanthin was one of the most senior magisters in the force Kael'thas sent to decimate Kirin'Var. It's only natural that he would claim my familiar as a kind of trophy.
I'm certain that Kanthin, fool that he is, has tried to compel Glacius to serve him. My scrying has revealed that Kanthin is now stationed at 'Manaforge Duro,' if that terminology has any meaning for you.