Vestments of the Warlock is a light armor set. When you cast an ability while under 33% Magicka, you restore 9000 Magicka. This effect can occur once every 1 minute.
A Stamina version of this set (Trappings of Invigoration) drops in Fang Lair.
The Vestments of the Warlock set is part of the base game. It drops in Selene's Web in Reaper's March. Each set item is bound on pickup. You can acquire light armor, weapons and jewelry of this set in the Breton motif style.