When you first approach him, he will say, "My name is Corim Ashlen, and I have the dubious honor of being the Loremaster of this Mage's Guild. Word has spread that you seek the Crystal Tower. I have known students of mine to search an entire lifetime, never destined to walk within its hallowed halls. I will however consider doing something I would have never thought to do. I will help you find the Crystal Tower. In return you must do a favor for me first. You see, a few nights ago priests of the Mad God attacked our Guild. They were protected by some sort of spell that absorbed our magic, making us powerless to stop them. Many of our initiates died, and the priests carried off a number of our treasured artifacts. Among these was a small diamond. I cannot speak more of this, other than to say it serves a vital purpose here in the Guild by strengthening our magic. It has a secondary function as well, one that would be of interest to you.
"I quested and won this magical gem in fair combat from its previous master, the Demi-Lich Zaraphus. It is said that the light from the gem will allow the viewer to see the true location of the Crystal Tower on a specially prepared map, a map I have in my study. The priests however have the diamond. If you would consider recovering it, I would be happy to show you the location of the Crystal Tower. You will however, have to bring me the diamond first. Do you agree?"
If the player agrees, he sends you off on the quest, "Good. You will find the Temple of the Mad God outside the city of Lillandril. Wait a moment while I get a pen and mark the location on your map. Remember, bring me the diamond and I will show you the location of the Crystal Tower as a reward..."
If they instead refuse, he says, "I truly wished you had agreed to help. I understand however that you may have other concerns. If you should change your mind, return here and ask me again about the Crystal Tower..."
When coming back after a refusal, he will say, "Welcome back, [player name]. I hope you have decided to try and recover the diamond from the priests of the Mad God. They probably do not expect a retaliation from us, so your chances of sneaking in are sure to be very good. You may run into their priests, but you look strong enough to deal with them. It shouldn't be too difficult to recover the diamond now. Do you agree?"
After the player obtains the diamond, Corim will be overjoyed, "Well done, [player name]. You have done this Guild a service it will not easily forget. I thank you for your efforts. Now, for my part of the bargain..."
But if the player comes back without the diamond, he will be far less happy, "[exclamation], the priests of the Mad God must truly be insane if they think they can get away with this sacrilege. [player name], rest until you are strong enough. You may try to recover the diamond again, when you feel up to it..."