Arelion's Mistress is the final quest in the Arelion's Journal quest chain.
With all the important matters at hand Arelion still found time in his schedule to see a mistress! It's all becoming perfectly clear. Viera Sunwhisper, that filthy wench... we'll show her to never cross a magistrix again. Take this scroll and find Viera. Find a way to lure her away from town and use the scroll on her. Arelion mentioned she couldn't resist a particular wine harvested by the cenarion druids. You might find some at Cenarion Refuge, just inside Zangarmarsh, west of here.
Excellent! That little backstabber won't be running off with anyone's husband any time soon. Here's a little something for your troubles. I trust we can keep this incident between us, <name>.
Upon completion of this quest you will gain:
After getting the quest, head to Cenarion Refuge and purchase a bottle of Viera's favorite wine, Cenarion Spirits, from Innkeeper Coryth Stoktron. Return to Falcon Watch and give the bottle to Viera (via the repeatable side quest  ). After leading her out of the gates, use the scroll on her.