Mary Quinn Mysteries

This series is also known as The Agency.

A Spy in the House

The Body at the Tower

The Traitor in the Tunnel

by Y.S. Lee

A young girl named Mary Lang is saved from her hanging from a girl's boarding school in London. She attends the school for five years, using her mother's surname, Quinn. When two of the teachers offer her a job as a spy, using the school as a cover, she happily accepts. Her first assignment is to be the paid companion of Miss. Angelica Thorold, a merchants daughter. Mr. Thorold is suspected of fraud, smulgglery, and other crimes, but can't be proven. Mrs. Thorold is an invalid, but goes out each afternoon to consult physicians. Mr. Thorold's assistant, Michael Gray, is a suspect of being an accomplice to his boss, but seems only to have eyes for Angelica: nothing more. When she teams up with the brother of one of Angelica's suitors, James Easton, they find out exactly what they need and more. 

I normally don't read mysteries, but it was so great! The characters were well-thought through and everyone was a suspect. I haven't read the third book and the fourth should come out in the next few months, but they're probably just as fabulous as the first two!! Mary's past is mysterious and every chapter you learn a bit more and more. Even at the end, you don't know about her totally, but I guess that's what mysteries do! Love them!