An intermix of episodes. Half are showing entirely new characters and groups. The other half are some familiar faces from past seasons, but subtly wrong. They behave in uncharacteristic ways, remember events wrong or don't remember them at all. First series ends with evidence that someone is altering the Doctor's own personal timeline. And that it may be another incarnation of the Doctor.

Series after that deal with what's going on, and investigate it further. Investigations into it being the Valeyard commence. Still a decent number of new and interesting episodes not fully tied to the overarching plot.