Enter Hearthglen and find a high vantage point from which you can see the town and gauge the Scarlet Crusade's forces, then return to Kirsta Deepshadow in Western Plaguelands.
What? Really? You want to know more? But you've already done so much for me, [player]. I couldn't possibly ask you to enter Hearthglen itself on my behalf.
Are you sure, [player]? Hearthglen is much more dangerous than the Pass--I cannot provide you any protection or even information about what you might face.
Well, if you really are willing to help, then enter the town and find a high place to gain a good view of the town. From there you can gauge their numbers and report them back to me. But be careful....