The opening chapters of this sensational novel focus on "Mercy Merrick," a nurse in the Franco-Prussian War. Mercy's post is taken over by the Germans. Mercy meets the emergency with great skill and aplomb, comforting the wounded soldiers and ensuring their safe passage. Her bravery is set in opposition to the cowardly surgeon and a timid English gentlewoman on her way to England to claim an inheritance from relatives who have never before met her.

In the midst of the battle, the English woman is killed. Mercy determines to take over the dead woman's identity and claim her inheritance. She successfully does so. However, it miraculously turns out that the Englishwoman was not dead at all, merely stunned, and she arrives in England looking for revenge. It is impossible for her to prove her identity until Mercy confesses. Even then, the reader has sympathy for the desperation that caused her to take on the impersonation and her story ends happily as she goes off to a happy marriage and to nurse orphans.