Many denizens of the Legion bestow gifts on their followers as you may well know. Some of these gifts the Dark Lady feels would be better off in her hands than in the hands of those with... lesser vision.
A sect of the Shadow Council hidden in caverns below Orgrimmar known as the Searing Blade are a prime example. The Lady tells me that members of the Searing Blade have come into the possession of two powerful spell books--she would like to "borrow" these books from them. You will get them for her.
Good, <class>. You have done well in serving the Dark Lady. Your continued perseverance and ambition will be of great use to the Lady's subjects. Return to me again in the future. Perhaps I will have other tasks for you that will aid the Dark Lady in her attempts at overtaking the Lich King and completely freeing the Scourge.