A Tome Truly Rare is a Chapter 3 side quest in The Witcher 2: Assassins of Kings, set in Loc Muinne. It revolves around the grimoire of the sorcerer Dearhenna, whose notes Geralt pieces together during The Secrets of Loc Muinne. The final piece, Dearhenna’s Notes IV, is carried by Adalbert and only drops if Geralt kills him at the end of that quest.
The grimoire itself is magically encrypted, so Geralt cannot make sense of it. He can keep it as a souvenir of his trip beneath the city or sell it to Bras of Ban Ard, a collector loitering in the marketplace. Do not expect a fortune: despite Bras talking up the price, the sale simply closes the quest. If Geralt let Cynthia use the megascope earlier, she outsmarts him and the book goes to Nilfgaard, leaving nothing to sell.
