Complex sentence: He was seated in the row ahead of Tintin and Captain Haddock and was astonished to hear the Captain mention the name "Calculus", showing that he was already planning to take over the moon programme that Calculus was working on.
Split into simpler sentences: He was seated in the row ahead of Tintin and Captain Haddock and was astonished to hear the Captain mention the name "Calculus". This shows that he was already planning to take over the moon programme that Calculus was working on.