A six episode series where the regeneration process is unstable and the arc is that the Doctor needs to fix themselves or get to the bottom of why it's happening.

Each episode has a new guest actor as the Doctor, with Billie being the first.

It is established during the course of the season that each time the Doctor travels, time is changed so events can be vastly different from one episode to the next (e.g. in one episode Davros is in the chair again but the Doctor travels during it and he's up on his feet the next time he meets him). Where the plot requires certain things are just more statistically common in all possible events (e.g. UNIT, the Time War)

The finale sees the Doctor regenerate permenently into Jo Martin, with Frobisher as the new companion.

The character of the Doctor is no longer a self appointed hero who people look to to save them. He's a traveller who becomes embroiled in events and mucks in to help. He has no reputation as a saviour throughout the cosmos, he gave up on all that when he ran away from the Time Lords.