The TARDIS breaks up with the Doctor. Like it strands him somewhere. This would be a multi-episode (possibly season-long) arc where the Doctor hitches rides with various aliens to find the TARDIS and figure out why it left.
He's still the protagonist, still saves the day and so forth, but we get to see him out of his element, maybe he grows and starts treating companions better.
Why does the TARDIS go away? Is it to protect the Doctor from the evil in the heart of the TARDIS? Does it gain foreknowledge of some villainous act on his part? Is it called away by the Black Guardian or some other cosmic being who wants to mess with the Doctor?
He's still the protagonist, still saves the day and so forth, but we get to see him out of his element, maybe he grows and starts treating companions better.
Why does the TARDIS go away? Is it to protect the Doctor from the evil in the heart of the TARDIS? Does it gain foreknowledge of some villainous act on his part? Is it called away by the Black Guardian or some other cosmic being who wants to mess with the Doctor?