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

This history-mystery series continues with another fine display of brains and bravery from the Wollstonecraft Girls—Ada Bryon Lovelace and Mary Shelley. Inspired fun for middle grade readers and fans of The Mysterious Benedict Society and Lemony Snicket!
 
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 new case is a puzzle indeed. It involves a horrible hospital, a missing will, a hasty engagement, and a suspiciously slippery servant.

But Mary’s stumbled onto a mystery of her own. She spotted a ghostly girl in a grey gown dashing through the park. A girl who is the spitting image of their new client.

The two cases must be linked . . . or else there’s a perfectly supernatural explanation.