While the Septim heir researches the enchanted book, Jauffre has a mission for you. You have to get rid of some suspicious spies wandering around the temple. Talk to Steffan, who will tell you where they usually meet at night. Go there and kill everyone. You'll find some keys when you search their bodies. Go to Bruma and talk to guard captain Burd. He'll allow you to legally search Jearl's house. Go there and enter the basement through a hatch on the floor. There you'll find a letter. Take it to Jauffre.