"A Letter Of Mary" is the third book in the Mary Russell series and the first one in which we see how Mary Russell and Sherlock Holmes function as a married couple.
They are both formidable people: Holmes, in his sixties, almost retired from a career he made largely in the previous century, but still with a restless hunger for the intriguing; Russell, an independent, wealthy, woman in her twenties, with a passion for scholarship and a tendency to lose herself in her books for days at a time. The two of them with an almost decade-long relationship that has moved from master and apprentice, through professional partnership and on to a marriage that is, to both of them, the defining aspect of their lives and yet the part of it that have the least knowledge and experience of.
They are serious, capable, responsible people. They can be intimidating, a fact they often take advantage of. They practice deception ruthlessly in the pursuit of their prey. Yet, together, they can laugh at their own hauteur and theatrics and they know each other so well that deception between them is impossible.
In "A Letter Of Mary" Russell and Holmes work to find the murderer of a friend, yet they spend most of their time apart, pursuing different prey and restricted in contacting each other because of the personae they have adopted for the hunt.
I found the overall tone of the book to be quite melancholic. The sources of the melancholy speak to the quality of the story-telling and character-building. The killing of the Russell's friend carries a real weight of loss at possibilities ended and produces an indignant anger, that sometimes flairs into wrath, at those who would take a life. This something that is often missing from detectives stories where the dead are just body-shaped puzzles to be solved. The second source of melancholy comes from the attacks on Russell and Holmes' way of living: their home is violated, they are separated for the first time in their marriage, they are forced to confront the new fear they now have of losing each other.
Russel and Holmes push through this melancholy with intellect and courage, powered by a strong sense of obligation to the dead woman and a refusal to give in to those who act against them. They are a source of strength to each other and their love is as deeply serious as everything else in their lives. I found it refreshing to see a commitment based on knowledge of the other person rather than a fog of romantic imaginings and hopes.
The plot revolves around the death of an older woman, a Gertrude Bell sort of woman, who runs archeological digs in the Middle East and occasionally acts in the service of the Crown.
There are multiple possible murderers to be hunted. Russell's hunt requires her to take on the persona of Mary Small and work as a secretary for a Colonel well known for his temper and his misogyny. Although this experience appears to require Russell to become someone else, the process and her reactions to the men she meets causes her to learn a great deal more about herself.
Much of the action in this book takes place off stage. The characters spend a great deal of time sitting together, sharing information and debating conclusions. The fights and threats of the two previous books are absent. I found this change of pace both refreshing and credible.
I believe that, with this book, the series crossed over the threshold where I will be less interested in the plots of the individual books and more concerned with the development of the relationship between Russell and Holmes and the insights they have into life and how it should be lived along the way.