Complex sentence: When, at the age of seventeen, the three pupils tired of learning and killed their teacher by magic they separated, with Zagor travelling north to Firetop Mountain, a peak he had seen in Demon-sent dreams.
Split into simpler sentences: When, at the age of seventeen, the three pupils tired of learning and killed their teacher by magic. After, they separated, with Zagor travelling north to Firetop Mountain, a peak he had seen in Demon-sent dreams.