This is a red version of the Nemesis lock set, and because it has no class restrictions can be transmogged by priests and mages too! These items all drop from The Burning Crusade instances, except the staff, which is a Blackwing Lair drop.
Vermillion Robes of the Dominant
Mantle of Three Terrors
Demonfang Ritual Helm
Gloves of the Deadwatcher
Sash of Serpentra
Staff of the Shadow Flame