Complex sentence: Once Tintin and his friends find their way out of the volcano, Kanrokitoff puts them all under hypnosis and summons a flying saucer piloted by the extraterrestrials; the hypnotised group board the saucer, narrowly escaping the volcano's dramatic eruption.
Split into simpler sentences: Once Tintin and his friends find their way out of the volcano, Kanrokitoff puts them all under hypnosis and summons a flying saucer piloted by the extraterrestrials. The hypnotised group boards the saucer, narrowly escaping the volcano's dramatic eruption.