Complex sentence: His ongoing storyline was that he has a secret from his past involviving practicising medicine while being struck off for assaulting a child which was exposed by Terence Turner who began blackmailing him.
Split into simpler sentences: His ongoing storyline is that he has a secret from his past: he is practicising medicine whilst being struck off for assaulting a child. This was exposed by Terence Turner who began blackmailing him.