Book of a Thousand Days by Shannon Hale

Dashti is a mucker girl from the Steppes. Muckers are a nomadic people who live in tents called ghers. Dashti has the gift of healing song, common to muckers and these songs are used to heal and help people with illness, depression and other ailments. She has just been sent to be the maid of Lady Saren, the daughter of the Kahn of Titor's Garden, one of the Eight Realms of this fantasy. On meeting her new mistress, she finds that Lady Saren has refused to marry the man her father has chosen for her. Her father has just told her that she will spend the next seven years locked in a tower for her willful disobediance. Dashti is given the choice, will she go with her new mistress or leave? She chooses to stay and help her new mistress all she can. They are taken to a tower in the wilderness where they are bricked inside with only a slit to let in air and a small trap door to throw out waste. There is a seven year supply of food and firewood. There are guards who keep watch, day and night outside. Dashti starts to keep a journal of their seven year stay in the tower, the Book of a Thousand Days. In this journal she records her life and her attempt to befriend and understand her distant mistress. She keeps a detailed account of their life in the tower.

One dark night when the guards are sleeping, they hear a voice outside the trap door. It is the young Kahn Tegus that Lady Saren has secretly promised to marry. But Lady Seran refused to speak to him. "You speak to him for me, Dashti! Pretend you are me! I cannot talk to him!" So Dashti talks with Kahn Tegus for several evenings through the trap door and discovers that he is gentle, kind and brokenhearted that Lady Seran has been put into this prison tower for seven years. When Dashti tells of their struggle to protect their food supply from the rats that have invaded their cellar, he returns the next night and brings them a cat. When he does not return, Dashti finds that she misses him very much.

One night a very disturbing voice comes through the trap door. It is Kahn Khasar, the one Lady Saren's father had chosen for her. Once again, Lady Saren has Dashti pretend to be her and talk with him. He threatens that if she should ever reveal his dark secret, he will kill her. Lady Saren is so frightened of this man that she falls into a deep depression and refuses to talk. Whatever his dark secret is, Dashti, too, is terrified of this man.

Soon after this, the guards are attacked and killed by a vicious wolf. The wolf tries to get in through the trap door, tearing at the opening with his strong jaws. Their cat pounces at the wolf and disappears.

The girls are left completely alone. Weeks and then a year goes by. The rats return to ravage their food supply and Dashti must make the decision that will change both of their lives forever. She plans to break out of their prison and go to the Realm of Kahn Tegus for refuge. Will they make it? What is the dark secret of Kahn Khasar? This version of an old Mongolian fairy tale will keep you enchanted until the final page. You will find Book of A Thousand Days in Teen Fiction.