The Scout Corpse is on the side of the road, just east of the Wellspring Flats Travel Stone. When you examine it you will be attacked by four Murderous Spirits.
Next, gather eight Corrupted Essences from Wicked Spirits.
When you have all eight, lay them on the Altar to the Vigil in Forlorn Fen. The Messenger tells you that all is not as it seems: The corruption of the spirits has been done intentionally. Also, he hints at a dark secret of the Farclan that the Vigil disapproves of, but does not tell you what the secret is.
Return to Borrin and report your progress.