Tintin, Captain Haddock and Calculus are on their way to Sydney for an international conference on space exploration. While their flight makes a refueling stop in Jakarta, they unexpectedly meet their old friend Piotr Skut (see The Red Sea Sharks for back story), who is now the chief pilot for eccentric millionaire Laszlo Carreidas. A short time earlier, the Captain had erroneously taken the somewhat disheveled Carreidas for a tramp and surreptitiously slipped him a five-dollar bill (which later is taken by the oblivious Professor Calculus, making the millionaire laugh for the first time in years). When introduced to Carreidas, the Captain inadvertently shakes the hand of the millionaire's secretary, the tall, aloof Spalding.
Unable to politely refuse Carreidas's offer of a ride on his prototype private jet, Tintin and his friends join the millionaire on the way to Sydney. Carreidas plays Battleship with the Captain, defeating him repeatedly by cheating with a hidden closed-circuit television camera and monitor. Unbeknownst to Carreidas and the others, Spalding and two of the pilots have been recruited to hijack the plane and bring it to a deserted island called Pulau-Pulau Bompas in the Celebes Sea. Skut is not involved in the plot, and so he becomes a prisoner too. After a rough landing, our friends are escorted out of the plane, and a terrified Snowy breaks out of Tintin's arms and runs off. Armed guards shoot at him, and a mortified Tintin takes him for dead.
A moment or two later, to Tintin's further shock, it turns out that the mastermind of the plot is none other than the evil Rastapopoulos, who declares that since "it's a bore to stop being a millionaire," it would be easier to simply take Carreidas's fortune. Accordingly, he has hatched an elaborate scheme to kidnap Carreidas and extract his Swiss bank account number. Captain Haddock's corrupt old nemesis, Allan, is working as Rastapopoulos's henchman. As for Tintin, the Captain and Calculus, Rastapopulous actually had no idea they would be accompanying the crotchety millionaire, but is nonetheless delighted to have the opportunity to exact revenge, and makes it quite evident that a very grim fate awaits our friends. Everyone is bound and held in Japanese World War II-era bunkers.
Meanwhile, Rastapopoulos takes a defiant Carreidas to another World War II-era bunker and has him strapped to a chair, to be subjected to the tender mercies of the malevolent Dr. Krollspell (a name possibly alluding to Adolf Hitler's quack doctor, Theodor Morell--"Kroll" is also the name of the Berlin Opera House where the Nazi Reichstag met). The corrupt doctor injects the millionaire with truth serum, so as to enable Rastapopulous to pry Carreidas's Swiss bank account number out of him. Unfortunately for Rastapopoulos, this plan quickly flounders. For Carreidas proves more than willing to tell the truth--about everything except the Swiss bank account. To Rastapopulous's fury, Carreidas launches into long disquisitions about his greedy, unscrupulous nature, boasting how he first stole a pear in 1910, at the age of four; shamed both his grandfather and his great-aunt to death; and has generally led a life of perfidy. Realizing the serum is defective, Rastapopulous becomes enraged and accidentally injects himself with the serum, becoming intoxicated. He too recounts hideous deeds in a boasting manner, calling himself "the devil incarnate". This angers the still drugged Carreidas, who begins an argument wherein both of the two men boast, rage, and quarrel over which one is the more evil. From what Rastapopoulos says under the serum's influence, Krollspell realizes that the crime boss intends to betray and murder him, not reward him as promised.
With the help of Snowy, who is not dead after all, Tintin and his friends manage to escape the bunker they are held prison in and find the bunker, high on the volcano, where Carreidas is held prisoner. Tintin captures Krollspell and Rastapopulous and escorts them to lower grounds. However, the serum wears off and Rastapopulous tries to escape. Later, they discover, thanks to a "voice" Tintin is hearing, a hidden entrance to a statue-filled cave. Knowing that they are in danger, as Rastapopulous is gathering the locals to pursue and kill them, they decide to enter the cave and they discover a large path, leading to the inside of the volcano. They enter the core of the volcano by triggering a mechanism. Rastapopulous and allies are not far behind, but they can not find the trigger mechanism which give them entrance to the core, so they use explosives to make their way.
Penetrating deeper into the volcano, Tintin and friends meet a strange man, Mik Kanrokitoff, a writer for magazine Space Week, who wears a transmitter on his ear and speaks with a heavy Russian/East European accent (he is the voice that has guided Tintin to the cave in which they are). He immediately notes that they are all in great danger, because the explosion has made the volcano unstable and it will soon erupt. They follow Kanrokitoff, who has the power to influence their minds, as he knows exactly where to escape. It is becoming hotter as they find their way out of the core of the volcano, and there is even a flow of lava that is threatening them, but they find a way up that leads to an exit. Carreidas pushes Haddock off the stairs, but fortunately Haddock grabs onto a stalagmite, narrowly escaping an imminent death of falling into fresh lava. The strange fellow uses his mind trick to calm Carreidas down.
Soon they find the way out and Kanrokitoff puts them all under his hypnosis. Kanrokitoff uses his transmitter, and apparent psychic powers, to summon a flying saucer, piloted by unseen aliens with whom Kanrokitoff is apparently familiar. The hypnotised group climb up a retractable ladder and board the saucer, which deposits them in a rubber dinghy, exchanging them for Allan, Spalding, Rastapopulous and the pilots, who are whisked away in the saucer. The group awakes from hypnosis and next thing they remember is that they are freed, and safe, but they cannot remember what happened to them. The party is eventually rescued, but only Snowy, who cannot speak, has any recollection of their alien abduction.
**** Further Information: Missing Pages of the Book ****
Hergé made an error when drawing the story: it was meant, like all Tintin albums, to be 62 pages long, but when he finished, it was found to be 64 pages long. Hergé's solution was to remove two pages from the end of the story, which covered the rescue of Tintin's group from the erupting volcano. The omission meant that the reader now sees a cliffhanger. At the bottom of one page a reporter on a seaplane watching the raft holding Tintin's group exclaims (in the English translation), "They'll be boiled alive like lobsters! We've got to do something." On the next page ("Thousands of miles away, several days later"), the story switches to Jolyon Wagg's living room as his family watches a TV interview of Tintin and associates.
----- Further Interesting Notes -----
1) The story seems to have been influenced by the "ancient astronauts" literature popular at the time, in addition to the mythology of a hidden ancient city in the South Pacific.
2) Laszlo Carreidas is based on aircraft manufacturer Marcel Dassault, although he clearly also displays some characteristics of another aviation legend, Howard Hughes (hypochondria, obsession with hygiene, hypercompetitiveness for example).
3) The prototype Carreidas 160, Carreidas swing-wing private jet, is a remarkable piece of design. Though not based on any real aircraft, it does have strikingly similiar design features shared with a number of different contemporary aircraft. The jet's swing-wings appear to be direcly modeled after those of the F-111. The undercarriage pods are similiar to those of Andrei Tupolev's jet transports. The tri-jet formula, merely an idea then, was implemented in private jet aircraft in the Dassault Falcon 50/500 series. Their intake geometry is reminiscent of the Rockwell B-1 bomber, a prototype at that stage. Other noteworthy features are the afterburning jet engines, shared with the Concorde, and a high set T-tail whose design is similar to the F-101 Voodoo.
4) Significantly, modern concepts of supersonic private jets also have triple-jet engines as their basis. Many aircraft designers who review the drawings of Carriedas 160 often remark on how very competent and finished the design is, and its practicality has been demonstrated in the form of fan-built free-flight and R/C models whose flying characteristics demonstrate a docile, swift transport which although never real, embodies the best in modern aeronautical design.