Complex sentence: Gemma Corwyn dies trying to prevent the Cybermen damaging the oxygen supply on the Wheel; and, shocked back to consciousness by her death, the insane Jarvis Bennett is mown down when he seeks revenge.
Split into simpler sentences: Gemma Corwyn dies trying to prevent the Cybermen from damaging the oxygen supply on the Wheel. Shocked back to consciousness by her death, the insane Jarvis Bennett is mowed down when he seeks revenge.