Complex sentence: As he works against the clock to solve the puzzle, he realizes a deadly plan is unfolding and is unwittingly caught up in a criminal conspiracy, one that carries life and death stakes for himself and his fellow passengers.
Split into simpler sentences: As he works against the clock to solve the puzzle, he realizes a deadly plan is unfolding and is unwittingly caught up in a criminal conspiracy. One that carries life and death stakes for himself and his fellow passengers.