3.5 stars. The mysteries Mary are solving (thefts at Buckingham Palace for the Agency, the murder of a nobleman by her presumed dead father) are interesting enough and some of the new secondary characters are fun. As always, I find the romantic plot line between Mary and James an annoying and contrived distraction from the other, stronger elements of the series. 
 ** detailed SPOILERS ahead for the end of the book** 
 At the conclusion of the book the heads of the agency split up and Mary is forced to choose whether or not to stay with Anne and the agency or go with Felicity to form a new detective agency that accepts male agents and takes different kinds of assignments. Mary instead decides to form an independent detective agency herself with her paramour James Easton. I felt this plot development superficially satisfying but frustrating on further reflection because it seemed very unrealistic that a woman of Mary's social standing (or lack thereof) would be able to develop the kind of relationships necessary to run a detective agency. She would need a lot of contacts and connections to both find clients and to go successfully undercover in sensitive areas. Even with her financial windfall I don't see how a woman in Mary's position could do this without the sponsorship of a group like the Agency.