Doctor Who: Peter Capaldi’s 9 Coolest Stand Alone Episodes
4. The Girl Who Died
Some threads take a long time to resolve, and sometimes to the point that they are exhausted. The Matt Smith saga suffered from this problem in bouts. The Capaldi age, by contrast, seemed to fly a great deal more by the seat of its pants, and so a long running mystery was wrapped up in mid-season stand alone style.
This thread was too intricate to overlook the fact that Peter Capaldi had already joined the Whoniverse, as an ill-fated occupant of Pompeii, way back in a David Tennant story. So the long running mystery of 'Why this face?' came to fruition. It might be true that Maisie Williams' character of Ashildr ultimately didn't come to much, but as a stepping stone for Capaldi's Doc, it was a great work. The Girl Who Died was a pivotal moment in the 12th Doctor's character transition, and marked an erasure of his meaner traits in favour of a far kinder, more fun loving version of himself.
Every good Doctor should end up a little different to how they started, and this ep was the prime turning point of Capaldi's character arc.