In the previous book, Professor Calculus had asked Tintin and Haddock to join him on his adventure to the Moon. After a series of events, the rocket had finally been prepared to take them to the Moon. But all was not safe. There was a chance that conspirators might foil the journey. Plus, mechanical faults would become fatal if not attended properly. The adventurers had fainted from
high-G after the rocket took off. Calls from earth-base sought for replies in vain.
Now, the rocket is accelerating out of earth's gravitational pull, into space. Snowy is the first to recover consciousness. He wakes up Tintin and the others. Calculus is excited on their journey.
But suddenly, the Thompsons pop out of nowhere. They come out, asking for the time when the rocket will launch. They are horrified to recieve the true answer. Professor is worried whether the oxygen supplies will last. Haddock is in a rage. He drives the two of them off, and settles for a drink.
Professor invites the Thompsons to look at Moon. But an accidental tug at a lever causes the rocket to stop moving and nutralize the gravity. Everyone starts floating. The captain is drunk and plays with his whiskey. Tintin manages to restart the rocket, bringing the gravity back.
Tintin goes to the Captain's deck to give him magnetic boots but finds it empty. Suddenly, someone opens the outer door and stops the rocket. tintin says to Calculus that the captain is behind this and goes out to investigate. Haddock is seen floating metres away from the rocket. Tintin realizes that an asteroid is pulling him away. Tintin instructs prof. Calculus to drive the rocket towards the asteriod to save Haddock. Calculus obeys. Tintin manages to rope Haddock and bring him back on the rocket.
They re-enter the rocket and find the Thompsons having overgrown beard and hair. Suddenly, an alarm sounds, warning them of an approaching meteorite. To their astonishment, the rocket steers itself clear of the object. Haddock sets to work on the Thompsons' hair. Calculus warns them that the rocket will nutralize gravity as it turns on its axis. It does so quickly.
They have a slight argument onboard. Calculus orders all of them to lie down, as tne rocket decelerates for landing on the Moon. The gravity rises inside the rocket. Tintin is the last to stay awake and contact earth-base before passing out. After a few seconds, the rocket lands on the Moon. Everything is quiet.
In a few minute's time, the adventurers call back to earth. They say that Tintin is geared up to step onto the Moon. Within a minute, Tintin does so. Haddock and Calculus follow him. But they are surprised when the outer door of the rocket suddenly closes and the ladder is retracted. It opens again and Frank Wolff comes out, apologising.
Over the next few days, they unload equipments onto the moon's surface. Calculus barely escapes another accident. The Thompsons start their adventure on the Moon. They prepare a tank to roam about the surface of the Moon. Tintin and captain go for a test drive and narrowly miss falling into a crevasse.
Afterwards, Tintin, Haddock and Wolff go for another drive. They stop in front of a cave and Haddock, Tintin and Snowy go into it. Inside the cave, Snowy falls from a precipice. Tintin goes after him and finds him slipping upon a layer of ice. Tintin arranges to take him up but almost sacrifices his life when his cylinders' oxygen levels go down.
The next day, Calculus, Hadock and the Thompsons go for a drive. Inside the rocket, confusion ensues. Colonel Jorgen surfaces and knocks out Tintin, immobilizing him. He orders Wolff to start the rocket for take-off. Out of fear Wolff obeys. He starts the rocket. It starts flying up but suddenly loses power and falls back onto the ground. Tintin confronts the two of them with a gun, saying that he stopped therocket from going.
By this time, the explorers have returned. Haddock ties up Wolff and Jorgen. Wolff reveals his story and the conspiracy. They are then tied downstairs. Calculus worries that the rocket has incurred damage and will take time to repair, all the while taking a toll upon precious oxygen.
After three days, the rocket finally takes off. The explorers pass out due to high-G forces. Suddenly they recieve a call from earth-base that they are heading off-course. Calculus wakes up and fixes the direction.
Suddenly, Jorgen intervenes. He holds a gun and threatens to kill them. But wolff comes up behind him and engages him. They tussle and Jorgen shoots himself. Tintin tells Wolff that he has regained their trust. Haddock is still suspicious.
A few hours later, Wolff disappears quitely. He goes downstairs and never re-appears. Suddenly the rocket stops. Tintin and Haddock go down to check, and finds Wolff's letter. He has made his ultimate sacrifice to save their lives, he has gone out into space, never to return.
Tintin knows that they are having breathing problems with Carbon Dioxide build-up. All the others pass out. But he stills struggles to keep awake.
After the turning mechanism occurs, Tintin is alerted to switch on the auto-pilot. Tintin tries to but falls down unconscious. He is woken up by a high-pitched signal. He manages to engage auto-pilot at the last moment, before passing out.
Mr. Baxter goes to the landing site to investigate. But improper timing lands his car beneath the rocket's exhaust. The rocket lands. Mr. Baxter comes out with superficial injuries.
They cut out a panel in the rocket's side and enter inside. Then they bring everyone out. Tintin wakes up but finds Haddock in a serious condition. But a mention of whiskey suddenly wakes up Haddock.
Others come. All the explorers rejoice. Calculus promises that he will go back to the Moon. Haddock is outraged and interrupts him, telling that Earth is their proper place.