Clara and Saffie have an imbalance in their friendship, Saffie goes through a realisation and comes to terms with the fact there’s something wrong with their relationship and finds the strength to move on.
The Doctor is a Time Lord: a 900 year old alien with 2 hearts, part of a gifted civilization who mastered time travel. The Doctor saves planets for a living—more of a hobby actually, and the Doctor's very, very good at it.