John Walters by Sapper delves into the world of espionage and adventure, set against the backdrop of World War I. The novel follows the protagonist, John Walters, a British officer who finds himself embroiled in a dangerous mission behind enemy lines. Sapper's writing is characterized by its fast-paced narrative, vivid descriptions, and intricate plot details that keep the reader engaged throughout the story. The book serves as a prime example of early 20th-century adventure literature, popular during the time of its publication.