Tintin''s friend Professor Calculus has been secretly commissioned by the Syldavian government to build a rocket ship that will fly from the Earth to the Moon. Tintin and Captain Haddock agree to join the expedition even though Captain Haddock shows considerable reluctance. Upon arriving in Syldavia they are taken to the Sprodj Atomic Research Centre called simply "the Centre" headed by Mr. Baxter. They are escorted by the "ZEPO" (Zekrett Politzs) a special security force charged with protecting the Centre from outside threats. While working for Syldavia Calculus is assisted by engineer Frank Wolff who works in the Centre and accompanies Tintin and Haddock around the facility. Prof. Calculus reveals that the Syldavian government invited nuclear physicists from other countries to work at the Centre which was created four years earlier when large uranium deposits were discovered in the area. The Centre is entirely dedicated to peaceful uses of nuclear energy. Calculus heads the Centre''s astronautics department since this is his primary area of expertise.