This scene
If nothing else before this had locked in that this era of Doctor Who was going to be incredible – this episode was it.
No Moffat-isms that made the Doctor or the Companions the special center of attention, nothing. The Doctor didn’t interfere, didn’t give Rosa Parks the magical courage to be a hero for standing up for what she believed in, nothing. The Doctor and her companions were just there, involved but just background to the amazingly powerful thing that Rosa Parks herself did.