On the island of Caer Darrow lies Scholomance - a wretched center of Scourge necromancy and evil.  Our enemy dwells within, conducting unspeakable acts of depravity on unwitting victims... at least, we surmise as much.  A door bars the way, and try as we might no entry is to be had without a proper key.$B$BAlchemist Arbington is well versed on Scholomance, and has an idea how to obtain a key.  You have proved your worth to me, and now I entrust this task to you.  Speak with him on this matter.