Complex sentence: They stroll arm in arm to join the party, but when Koenig catches sight of the Earth visitors, he reacts violently, treating them as grotesque alien monsters and ordering Weapons Section to destroy the'alien' ship.
Split into simpler sentences: They stroll arm in arm to join the party, but when Koenig catches sight of the Earth visitors, he reacts violently, perceiving them as grotesque alien monsters. He orders Weapons Section to destroy the'alien' ship.