In a frontier cottage during the Franco-Prussian War Mercy Merrick and Grace Roseberry meet and their destinies become intertwined as Mercy serves devotedly as a nurse while carrying the burden of social stigma and poverty, sudden violence and the arrival of a German surgeon intensify the crisis and when Grace falls into mortal danger Mercy yields to temptation and assumes her identity, after which the scene shifts to Mablethorpe House in England where Mercy is welcomed as Lady Janet’s companion yet news from Germany and the ominous approach of a mysterious man foreshadow the gradual exposure of her secret and deepen the unfolding tension.