The Secret of the Swordfish was first published in Tintin magazine from the very first issue in September 1946 on.
Part 1: The first volume, "Ruthless Pursuit," opens on the eve of the Third World War. Details are scarce, but we are told that the enemy is a totalitarian Asiatic superpower known as "the Yellow Empire," ruled by the Emperor Basam Damdu, and that the Yellow Empire and the free world have been locked in a cold war for the past three years. Within the first few pages of the book, the Yellow launch a worldwide aggression with rockets, bombers and paratroopers that quickly destroy and conquer the world''s other major powers. However, the British military has been secretly working on a new type of superweapon known as the Swordfish, in anticipation of the war; when the Yellow attack is launched, the two protagonists, Captain Francis Blake, a British officer, and Professor Phillip Mortimer, the scientist developing the Swordfish, escape with the superweapon''s plans and seek asylum at a secret base where they will be able to finish their work. The rest of the episode follows their attempts to escape the pursuing Yellow forces, led by the cunning and conniving Colonel Olrik, Basam Damdu''s chief of security. They initially escape from Britain in a jet-powered airplane known as the "Golden Rocket," but are shot down somewhere over Iran by Yellow interceptors. They must continue the trek to the Strait of Hormuz on foot. Along the way, they encounter resistance fighter Ahmed Nasir, who becomes an invaluable help to them, and finally seek refuge in a small town in the Herat province. One of their hosts there betrays them, however; the episode ends with the Yellow storming the city but finding the two Britishers gone.
Part 2: "Mortimer''s Escape" takes place in two distinct halves. The first one picks up right where "Ruthless Pursuit" left off. The enraged Yellow commander orders his troops to search the city until they find Blake and Mortimer; however, he then executes one of the community''s elders when the latter refuses to cooperate. This sparks an immediate insurrection in which the outraged townsmen quickly massacre the Yellow troops; in the ensuing chaos, Blake and Mortimer emerge from hiding and take off again, still with Nasir helping them.
Eventually, the three of them make it to the Strait of Hormuz, but Blake is injured and loses the documents while trying to escape a Yellow patrol. Mortimer then tells Nasir to take Blake to safety, while he returns to search for the plans. He is himself then captured by Yellow troops, but not before he is able to find and conceal the plans. The second half of the episode begins three months later, with Colonel Olrik making a report to the high council of the Yellow Empire. It is clear that the Yellow are having a lot of trouble controlling their new empire; rebellions, dissident movements and acts of terrorism have continued worldwide, and despite their best efforts, the Yellow have still not been able to sweat the Swordfish plans out of Mortimer. As chief of security for the Empire, Olrik is the natural scapegoat for this state of affairs; he therefore decides to take the gloves completely off and torture Mortimer as harshly as necessary, hoping that his confession will help save Olrik. Under instructions from Nasir, who has managed to infiltrate the detention center, Mortimer pretends to relent, and agrees to reconstitute the Swordfish plans for the Yellow. After this, we are finally shown the secret base, where Blake and the admiral in command, Sir William Grey, have been conducting resistance against the Yellow (including many of the incidents that Olrik is being blamed for). They now have two urgent priorities; first, to find the lost plans and second, to break Mortimer out of prison. The first problem is resolved when Mortimer is able to pass a message to Nasir telling him where he hid the plans. Soon after this, Mortimer almost prison break on his own; before the Yellow are able to capture him, he is rescued by Blake and Nasir personally, who then take him to a submarine and manage to escape, despite the Yellow navy and air force''s best efforts.