The story is told through the eyes of the three main characters, Queen Mary and her two "jailers," George Talbot, Earl of Shrewsbury, and his wife, Bess (Elizabeth Talbot) of Hardwick. This gives you a bit more understanding of their own position in this time of captivity.
The Other Queen begins with Mary Stuart, cousin to Queen Elizabeth, arriving in England after having fled her country, expecting Elizabeth to restore her to the throne of Scotland. She has lost the love and support of her people by marrying the man believed to have killed her previous husband. Elizabeth, however, puts her in the custody of George Talbot and his wife Bess of Hardwicke as a result of Mary's repeated attempts to claim to English monarchy for herself. Mary is indignant at the captivity, repeatedly stating her claims to royalty, and is upset when she is given some of the reigning queen's gowns to wear, saying that they are "hand-me-downs." She is unafraid of punishment for any reckless or insulting behavior she makes to her cousin, believing that one would never execute a fellow monarch. Most of the novel centers around the first few years of Mary's Stuart's imprisonment, during which time she makes several failed escape attempts and almost immediately begins to seduce the earl. George slowly begins to feel his loyalty to Elizabeth fade, replaced by a strong attachment to the captive queen. This results in marital problems with Bess, who ultimately separates from him.
For an excellent book review, The Tudor Book Review site has in-depth article.
This website is excellent at listing and reviewing books of the Tudors and other books of history.