The story continues from Destination Moon. Calculus is taking Tintin, Tintins dog Snowy, Haddock and his assistant Frank Wolff to the moon in his rocket. However, Thomson and Thompson come up from the hold, having mistaken the time of the launch (1:34 a.m. on Tuesday, June 3, 1952). Calculus is concerned at the effect this will have on their air supplies- Haddock is furious, and lambasts the Thompson twins for being too imbecilic to understand the difference between 1:34 a.m.
and 1:34 p.m.The journey to the Moon is not uneventful--Haddock has smuggled some whisky in hollowed-out books, becomes drunk, and engages in some unscheduled extravehicular activity that results in him briefly becoming a moon of the asteroid Adonis. Tintin must also don a space suit to fetch him, and, in a very rare display of temper, lashes out at the Captain, declaring that the latters recklessness has nearly cost us our lives. When the rocket must temporarily halt in order to execute the turnaround maneuver that will enable it to land on the moon right side up, the momentary lack of natural gravity also poses problems for Haddock, who neglects to put on his magnetic-soled boots in time.Additionally, the Thompson twins suffer one of their periodic relapses of the condition caused by their ingestion of the energy-multiplying substance Formula Fourteen (see Land of Black Gold).
As a result, they sprout thick hair that grows at lightning speed and frequently changes color. The Captain, having no other immediate duty, volunteers to cut their hair, but can scarcely keep up with it, and begins to suffer blisters from the scissors. He remarks sarcastically that in future, when people ask him what he did on the rocket, he will reply, Me? I was the hairdresser! Gradually, however, the twins condition abates, and their appearances begin to return to normal.The spacecraft lands safely in the Hipparchus Crater, and by agreement of the crew, Tintin is the first to set foot on the Moon - the first human to do so.
Everyone then gets a chance to walk about- even the Captain enjoys it, but upon seeing the Earth, expresses fear about whether they will survive to see it again.The crew soon starts unpacking the scientific payload (telescopes, cameras, and a battery-powered tank), finishing the work at 23:45 Earth time on June 3. Calculus decides to reduce the total stay on the lunar surface from 14 Earth days to 10 in order to conserve oxygen.
Three days later, the Captain, Wolff and Tintin take the battery-powered tank to explore some stalactite caves in the direction of the the Ptolemaeus Crater- Snowy falls on an ice sheet, damaging his two-way radio and there is a minor drama in rescuing him, but they return to the rocket safely.Tintin decides to rest up and have lunch with Wolff while the Captain, the twins and Calculus immediately go out in the tank again on a 48-hour trip to explore the lunar caves in detail as Calculus suspects they might find uranium or radium deposits there.A sudden turn of events occurs when the spy plot briefly overlooked in Destination Moon is revealed.
A secret agent from a foreign power, the brutish Colonel Jorgen, whom Tintin had previously encountered and bested in King Ottokars Sceptre, has been hiding in the rocket since it was launched eight days previously (having been smuggled aboard along with technical equipment).
Wolff reveals his history of gambling debts, which Jorgens employers have used to blackmail him into aiding them involuntarily.When Tintin goes below to fetch some supplies for lunch, Jorgen knocks him out and tries to seize control of the rocket, which he plans to fly back to his own country, leaving the others marooned on the Moon.
Outside, from the moon tank, the Captain, the Thompsons and Calculus watch, horrified, as the rocket blasts off, shuts down, and, for one horrible moment, appears to be on the verge of collapsing before coming to rest right-side up.
Tintin has freed himself and succeeded in foiling the plot, but in order to do so has been forced to sabotage the rocket to prevent Jorgens attempted liftoff. After the group interrogates Jorgen and Wolff, Tintin eventually locks the spy in the hold, against protests by the Captain that they wont have enough oxygen to last the journey home unless they abandon him on the Moon or kill him.
Calculus determines that the crew needs at least four days to repair the damaged rocket while the remaining oxygen supply will last at most four days.Due to the strain on the oxygen supplies, the crew decides to abandon some of the equipment, rather than disassembling it and packing it up, and to cut short the lunar stay. The repair work is completed slightly ahead of schedule after three days, and the rocket cleared for lift-off 4:52 PM Earth time as the sun sets over the Hipparchus Crater.
Even so, shortly before take-off, the Captain becomes the first among them to experience a bout of dizziness due to build-up of carbon dioxide. The lift-off is successful, but the rocket is off-course, and by the time the crew awake from the liftoff-induced blackout and correct it, they have lost additional time and consumed yet more oxygen.Halfway back to Earth, Jorgen escapes after overpowering the Thompsons, who had gotten the idea into their heads that handcuffs would be more secure than the Captains knots.
When Wolff sees that Jorgen intends to shoot Tintin and the others, he tries to dissuade him- the gun goes off accidentally, and Jorgen is killed instantly. The crew have no choice but to consign the body to space. However, even without Jorgen, now there isnt enough oxygen to make it home.
Overcome with guilt, Wolff opens the airlock and lets himself out into space to save the others lives whilst they are sleeping, leaving a moving farewell note.The rest of the group continues towards Earth, as their oxygen runs low. Everyone falls unconscious. Tintin faints but mission control sounds a piercing tuning signal which awakens him, allowing him to set the rocket up to land.
After the ship lands, firemen break the door open, finding everyone unconscious. On the tarmac, everyone is revived, except for the Captain. A doctor is giving a prostrate Haddock oxygen, but fears that his heart is worn out because It seems he was a great whisky drinker. Suddenly roused by the sound of the word whisky, Captain Haddock wakes up with a start.
Everyone rejoices and a ground crew member returns with a bottle of whisky. Calculus gives a toast which includes his hopes for a return to the moon. The Captain gets furious and promptly walks away, resulting with a trip and a fall over a stretcher in the midst of declaring that Mans proper place ... is on dear old Earth!