Tintin, Captain Haddock, Calculus, the Thompsons' and Wolff uncover the wonders of the moon. They also discover another person aboard the rocket ship who threatens to leave them all stranded on the moon.
Tintin and Captain Haddock have been asked to be part of the expedition to the moon. As they help Professor Calculus prepare for the launch, Tintin persists in finding the internal spy.