Complex sentence: The head of the complex, Professor Watson remains at his post when the reactor goes critical, and offers the Doctor aid and advice in trying to get to Sarah despite Carter attempting to stop the Doctor before he fell to his death.
Split into simpler sentences: The head of the complex, Professor Watson, remains at his post when the reactor goes critical. He offers the Doctor aid and advice in trying to get to Sarah Jane despite Carter attempting to stop the Doctor before falling to his death.