Professor Calculus, Tintin, Snowy, Captain Haddock, and Calculus' assistant Frank Wolff are aboard an atomic rocket-powered spacecraft leaving the Earth bound for the Moon. Soon after takeoff they discover that the detectives Thomson and Thompson have accidentally stowed away onboard, putting a strain on the oxygen supply. The detectives accidentally turn off the nuclear motor, disrupting the artificial gravity and sending everyone floating until Tintin corrects the problem. They then suffered a relapse of the Formula 14 drug (seen in Land of Black Gold (1950)), resulting in their hair growing rapidly in multiple colours. Calculus subsequently administers a cure. Haddock, who has smuggled whisky aboard the rocket, gets drunk and takes an impromptu spacewalk, during which he briefly becoming a satellite of the asteroid Adonis (at which point, Professor Calculus humorously says he will tell Earth that Adonis has a new satellite by the name of Haddock) but Tintin is able to rescue him.[1]
The rocket lands in the Hipparchus Crater, with Tintin being the first human to step on the Moon. Three days later, Haddock, Wolff and Tintin take the battery-powered tank to explore some stalactite caves in the direction of the Ptolemaeus Crater; inside a cave Snowy slips into an ice-covered chasm, but Tintin rescues him. Later aboard the ship, Tintin is overwhelmed by a third stowaway, Colonel Jorgen, a spy who had been smuggled aboard by Wolff, who has been blackmailed by a foreign power for which Jorgen works. With Wolff's help, Jorgen seeks to hijack the ship and return it to Earth, but through emergency sabotage that cuts power to the engine, is foiled by Tintin.[2]
Due to the strain on the oxygen supplies, the crew decides to abandon most of the equipment and to cut short the lunar stay. The repair work is completed slightly ahead of schedule, and the rocket cleared for lift-off. Halfway to Earth, Jorgen escapes his bonds thanks to the detectives' bungling and tries to kill Tintin; Wolff seeks to prevent him, and in their struggle over a gun Jorgen is killed. When it is revealed that there will not be enough oxygen aboard for the crew to survive the journey, Wolff sacrifices himself by opening the airlock and floating out into space to his death. The crew fall unconscious but Tintin wakes long enough to set the rocket to auto-pilot and it arrives back in Syldavia safely.[3]