John Durward and John Trenchard are two Englishmen who join a company of Russian doctors, nurses, and orderlies working on the Russian side of the Eastern Front at the height of World War I. Durward, the primary narrator, is a detached and seemingly-objective observer of events; his friend Trenchard is a dreamy, clumsy, and naive man whose fiancee, Marie Ivanova, is serving alongside him as a nurse.

The narrative follows the unlikely group as they are embedded in the Front, treating casualties and cholera victims while dodging shellings and enemy ambushes. At first the group seems to get along well enough, until Semyonov, a dark, charismatic, hyper-masculine doctor in their company, sets his romantic sights on Ivanova.

As the medics desperately try to fulfill their duty among the brutal backdrop of the war, their intricate relationships become the centerpiece of a complex emotional narrative that winds through the dark forest, a symbol of the confusing shadows that can lie between even two people bonded by wartime.

Walpole served in the Russian Red Cross on the Russian-Austrian front during World War I, and his real-life experiences are reflected in the narrative. On its publication The Dark Forest was called “the best picture of life in a field-ambulance on the Eastern Front that has yet been written” by the Saturday Review, and it was popular enough for Walpole to write a sequel, The Secret City, which went on to win the James Tait Black Memorial Prize for Fiction.