Tintin, Capt. Haddock and Snowy arrive at Marlinspike. They meet Nestor and are surprised to hear that Professor Calculus has left a few days before, without telling his whereabouts. Just then a telegram arrives. Haddock sees that Calculus has written to them, requesting them to meet him in Syldavia. Tintin, Haddock and Snowy leave.
After two days, they fly to Syldavia. The captain is disgusted with the whole country offering only mineral water. He pays heavy import duty for his whiskey. A cab driver meets them, saying that Calculus has arranged for a car to take them to his place at Klow. They drive away.
Tintin sees that a car is following them since they left airport. Then he sees that the Driver is not taking them to Klow. He demands an answer and the driver replies that Claculus lives at Sprodj. From then on, Tintin and Haddock encounter numerous checkpoints.
Finally, they arrive at Sprodj. They drive into a building disguised as a garage. A senior engineer meets them, introducing himself as Frank Wolff. To the captain's question, he answers that the car following them had special security ZEPO men. He then takes them to see Prof. Calculus.
Calculus is testing a helmet, when he sees his friends. He is delighted to see them. Tintin sees that Calculus is using an ear-trumpet for hearing. Calculus starts talking. He says that he has planned an exploration to the Moon, and is currently designing a rocket for the journey. He has invited them here to join him in his adventure. Haddock is furious and starts abusing him. Calculus misinterprets his abuses for congratulations and thanks Haddock heartily. The Director General of the centre, Mr. Baxter arrives and meets them.
At night, a fire alarm sounds. The fire department retrieve Captain Haddock in a furious state. He shows them the ear trumpet( he mistook it for his pipe) and the smoke it had caused.
The next morning, Frank Wolff shows them around the main workshop, the nuclear testing centre and finally, the test rocket. He goes away when Calculus comes. Calculus starts explaining the details. He suddenly becomes emotional and bumps into a painter. The bump distracts the painter, spraying Haddock with paint.
One week later, the radar operators are suddenly alerted to the presence of an unidentified aircraft. Parachutists jump from it and land outside the centre. Sentries patrol the centre in their search.
The Thompsons enter the centre under arrest. Tintin recognizes them inspite of their disguise and vouches for them. They are released.
Next morning, Tintin goes for a walk. He sees two ventilators, vulnerable points for enemy approach. He encounters some bearcubs and drives them off, before settling in a ventilator's proximity. Night falls. Tintin is suddenly alerted to an enemy. He tries to stall him, but is shot from behind.
Inside the centre, there is a fuss. There has been a power-cut in an area and Haddock has been knocked out. The others cannot find out how it happened.
Elsewhere, in Borduria, plans go on inside a secret organization to seize the Syldavian rocket during its flight.
The Thompsons explore the centre in search of mystries and run into scintillating experiences.
In a few weeks, Tintin recovers from his wound. The day for the test flight of the rocket arrives. Tintin has coaxed Calculus into rigging up a remote explosive inside the rocket. The rocket launches. Within minutes, it reaches the Moon. All watch in awe.
As the rocket reappears from an orbit around the moon, the Bordurian organization intercepts control. The rocket flies out of its specified path. Calculus suddenly realizes that his fears were correct. He triggers the explosive but to no effect. He becomes uncontrollable. Tintin reconnects two wires and triggers the explosive. The rocket explodes in flight. Calculus is sad over the destruction of his work, but Tintin consoles him, emphasizing their achievements. He says that the Professor may start work on the real rocket.
Days go on. A space-suit is being tested with the captain as guinea-pig. THe suits contain some mice and they tickle Haddock so that he jumps about. When his helmet is unlocked, the mice run out. The captain is furious and he calls Calculus an "old goat".
Claculus hears the remark and becomes uncontrollable, shaking with rage. He orders Haddock to follow him. Any security who gets in his path runs for his life. Calculus seats Tintin and Haddock in a jeep and reparts the centre without permit. He drives them to the rocket building centre and shows captain, the goat's work.
They enter the rocket. The Professor shows them around inside the rocket. But he suddenly falls through a port-hole. The falls leaves him shaken and he suffers amnesia.
Mr Baxter is about to go mad over the news of Calculus' amnesia. The captain tries his best to recover Calculus but his attempts fail. Finally, he makes a remark about "goat" again. Calculus hears it and suddenly recovers. Later he thakns Haddock for saving him from amnesia.
The day for the launch arrives. Mr. Baxter gives a fine speech. The captain makes a scene over a bottle of Champagne, but finally opens it. They drink to health.
Finally they get inside the rocket. The explorers: Cuthbert Calculus, Frank Wolff, Tintin, Captain Haddock and Snowy. Every character experiences his worst fears. The rocket launches.
A heart-rending G-pull renders all of them unconscious. Upon earth, the Syldavians pray for their safe journey. THe radio-operators reach out for answers but in vain... What happens next?