I must apologize for my ignorance, but even though I have wanted to watch this show because from what I've heard it's very good, I have not had the chance to. 11th, 12th, and 13th doctor? Regeneration, did he get assimilated or something? If someone could give me some rough incite into what is going on, it would be greatly appreciated.
Sorry for the confusion, but the show is still only up to the 10th Doctor.
This story is about (for the moment at least) a future version of the Doctor and his companions.
The current and past Doctors will get their turns in the story as well (eventually).