Book of a Thousand Days by Shannon Hale
On her very first day as a lady’s maid, Dashti inadvertently agrees to stay with her lady as she is imprisoned in a tower for seven years for refusing to marry the man her father chose for her. Having been taught to read and write, Dashti keeps a journal of the endless time she and Lady Saren spend in the tower. They are visited by Khan Tegus, with whom Saren had been communicating and agreed to marry. Too frightened to speak for herself, she orders Dashti to pretend to be her, and Dashti finds herself falling for the khan. But then Lord Khasar, the evil man Saren was meant to marry, attacks the tower leaving them utterly alone without even their guards. They manage to escape and travel to Tegus’s land, but still Saren refuses to reveal herself.
Part historical fiction, part fairy tale, this gentle read is recommended for middle school and up.