Complex sentence: Wendell asks David to follow Francis, as he is the only one capable of persuading him to return, and Francis, seeing an open wound, is unable to control his bloodlust and he kills the girl and feeds off her.
Split into simpler sentences: Wendell asks David to follow Francis as he is the only one capable of persuading him to return. And Francis, seeing an open wound, is unable to control his blood lust and he kills her and feeds off her.