An Invader's Scourgestone is the insignia of the Scourge's elite troops.  These are sometimes found on the stronger of the troops positioned in the Plaguelands.  Slaying such a creature is indeed a challenge, but one that should be relished with a commission to vanquish evil.$B$BThe Argent Dawn currently offers a valor token in exchange for ten of these insignia.  Bring them to me here, and I will make sure you receive your just reward.