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.