The Dark Frontier (1936) is Eric Ambler's first novel, about whose genesis he writes: "[…] Became press agent for film star, but soon after joined big London advertising agency as copywriter and "ideas man". During next few years wrote incessantly on variety of subjects ranging from baby food to non-ferrous alloys. Have travelled in most countries of Europe, been stranded in Marseilles and nearly drowned in the Bay of Naples. Decided, on a rainy day in Paris, to write a thriller. Result was The Dark Frontier."

The novel is set in the mid-1930s (1934 or 1935) in Ixania, a small (fictional) country somewhere in a mountainous region of the Balkans bordering Romania. There, a peasant revolt succeeds in overthrowing the country's dictatorial regime and in establishing freedom and justice for all its citizens. Throughout modern history Ixania, a "God-forsaken country", has preserved its political independence because of its lack of natural resources and, generally, its comparative irrelevance in economic matters. However, through the defection from Nazi Germany of Jacob Kassen, a nuclear scientist, the Countess Schverzinski and her brother, Prince Ladislaus, who effectively run the country, are in possession of a formula to build an atomic bomb (the "Kassen secret"), a fact they want to exploit for their country's but also their own personal benefit.

Two groups of people want to prevent exactly that. There is Simon Groom, a representative of Messrs. Cator & Bliss Ltd., a British armament manufacturer, who is sent to Ixania to get hold of the Kassen secret by hook or by crook. He enlists the services of Professor Henry Barstow, an English physicist who is to travel with him to Ixania to determine whether the secret papers whose theft he plans to commission are authentic and worth the money. However, Henry Barstow seems to be a cover name for Conway Carruthers, a superhero who has realized that the Kassen secret poses "a serious menace to world peace" and who, accordingly, has made it his job to rid the world of that danger by destroying all copies, and the original, of Kassen's papers. His mission is to prevent, once and for all, the manufacture of the bomb and to "preserve civilization". Carruthers's charismatic authority attracts the attention of William L. Casey, an American journalist stationed in Zovgorod, the capital of Ixania. Originally only interested in a good story, Casey becomes Carruthers's quasi-assistant, a change Casey himself describes as his "transition from newspaper man to desperado".

Siding with the peasant revolutionaries, Carruthers becomes the brains of the operation and thus the de facto leader of the peasants. On several occasions his and Casey's lives are in danger, repeatedly they are "standing in front of the wrong end of a gun", but it is always Carruthers's almost superhuman intelligence and skills that save them. Within only one day it turns out that, with the old government having stepped down, the revolution has been both successful and unbloody. Kassen is dead, and all copies of his secret except one have been destroyed. The one copy that has survived is Countess Schverzinski's, and she is driving her Mercedes at breakneck speed along a dark and narrow mountain road, with the only intention of fleeing the country. However, Carruthers and Casey are following her in Groom's car (which they have nicked), but before they can catch up with her and stop her vehicle she has an accident, is catapulted out of her car, and dies. The wreck of her Mercedes catches fire, so all Carruthers has to do when he arrives at the scene is retrieve the last remaining copy of the bomb-building manual from the Countess's body and cast it into the flames.

It is an obvious fact that Ambler's subsequent novels are quite different from The Dark Frontier—not so much in subject-matter but most certainly in style and atmosphere. Critics as well as Ambler fans (and the author himself in an Introduction to the novel) have pointed out that The Dark Frontier was meant to be a parody of the brand of adventure thriller Ambler enjoyed as an adolescent but came to find rather silly when he reached adulthood. In other words, Ambler wrote an intentionally "bad" novel. However, since both the writers and the writing that is parodied have been long forgotten, it is difficult for 21st century readers to fully appreciate the book's intended comic nature. But there are some signs in the novel that somewhat elucidate Ambler's intention, for example Carruthers's unrequited, and absurd, love for the evil Countess Schverzinski, which makes him want to put a bullet through his head when he finds out that she is dead, a suicide which can only be prevented through Casey's intervention.

Based on the development in weaponry of the year 1936, The Dark Frontier is one of the first novels to predict the invention of a nuclear bomb and its consequences.

See also

• History of nuclear weapons
• List of modern armament manufacturers
• Stock character
• Crime fiction