The Case of the Girl in Grey (The Wollstonecraft Detective Agency, Book 2)

Now in paperback, a second comic case to test the brains and bravery of the intrepid Wollstonecraft detectives–Ada Bryon Lovelace and Mary Shelley.
 
The Wollstonecraft Detective Agency was supposed to be a secret constabulary, but after the success of their first case, all of London knows that Lady Ada and Mary are the girls to go to if you have a problem.
 
Their latest case is a puzzler indeed: A dead father, a missing will, an escaped lunatic, and a hasty engagement. How does it all connect? With the help (and sometimes hindrance) of their sisters Jane and Allegra, these girls break codes, break a girl out of the hospital, and break up a very bad betrothal.