France, October 1918. Though the war is nearing its end, the German enemy refuses to go quietly. During a nighttime barrage, British stretcher bearers find an exhausted officer, shivering with cold and a loss of blood from several wounds, clinging to life at the foot of a tree shattered by shelling and gunfire. The soldier is brought to Bess Crawford’s aid station, where she stabilizes him and treats his injuries before he is sent to a base hospital. Surprisingly, the officer isn’t British—he’s wearing the tattered remnants of a French uniform. And even stranger, when he shouts out in anger and pain, he speaks in fluent German.

When Bess reports the incident to the hospital’s matron, her weary superior offers a plausible explanation. The soldier must be from Alsace-Lorraine, a province in the west where the tenuous border between France and Germany has shifted through history, most recently in the Franco-Prussian War of 1870, which was won by the Germans. Of course, Matron could be right. Still, Bess remains uneasy—and unconvinced. What was a French soldier doing so far from his own lines . . . and so close to where the Germans are putting up a fierce, last-ditch fight? And if he is Alsatian, on which side of the war do his sympathies really lie?

Before she can inquire further, Bess is wounded while helping to evacuate soldiers from the battlefield. Sent to Paris to recuperate, she discovers that her mysterious soldier is also in the French capital . . . but has disappeared. Could he have been the infamous German spotter for the “Paris Gun” that is the talk of the Allied Army? It had shelled terrified Parisians earlier in the year, then fell silent. Or could he be involved in some other dark treachery?