Complex sentence: He's so determined to leave his little island home behind that he stows away onboard a marvelous zeppelin--one that just happens to be loaded with treasure and is hijacked by a gang of ruthless criminals !
Split into simpler sentences: He's so determined to leave his little island home behind, that he stows away onboard a marvelous zeppelin. One unknownly, just happens to be loaded with a treasure and is hijacked by a gang of ruthless criminals!