Reaver's Unmentionables is a quest in Fable III which becomes available following the infiltration of Reaver's "secret society" masquerade party with Page. You can locate the quest giver by using the Sanctuary's map table's quest list (Y while on the map) to select "Reaver's Unmentionables" as the target quest and following the glowing trail. It is good to keep in mind that Balverines now inhabit the Millfields area, which makes it considerably more dangerous for those melee combatants with slow reflexes.