Deathstalkers in Shadowfang

In preparation for an assault on Shadowfang, two deathstalkers were sent to the keep to gather intelligence. It has been many days and they have not returned, but we must receive their report if we're to have any hope of a successful attack! So here is your task, <name>. Go to Shadowfang Keep to the south and find the Deathstalkers Adamant and Vincent. Find them, and if they require aid then give it. This mission is as dangerous as is it critical, <name>. Do not fail.