Harry was not sure if Severus looked like Christmas, Easter, and his birthday had come up wrapped in one because of his promise or because he was forgiven. Either way, he would count his blessings when the man hurried after him, awed by the library Salazar Slytherin had hidden in these tunnels. Reverently, Severus brushed over the shelves. Touching the books seemed out of the question. At least until his master explained, "I want to obliviate Frank and Alice Longbottom. I want to make them forget the night they have been tortured to insanity so that Neville can have his parent's back. Tom gave me a book that spoke about selective obliviation. But I can't make heads nor tail of it since it says that it is possible but doesn't give enough instructions as to the how. The Horcrux-Tom suggested this library, and since you are the only expert of the mind-arts I trust, here we are."