Alternate Doctor Who season 4 concept (starting from the end of season 3)
Season 3 would end more or less like it does in the show, the Master dies, the Doctor wails over his body and then we cut to black and, when it comes time to say goodbye to Jack and Martha is when things change a little because the Doctor doesn't invite Jack to come with him, and he takes Martha home before she says anything but she just accepts it like he knew she was going to anyway. And that's just how it ends, the Doctor flying away.
Then we start season 4 with the Doctor already with a new companion, and it's kind of jarring because we didn't get to meet him, he's just there and both him and the Doctor act like he's been there for a while. This happens during the special with the space Titanic and it's build up to make us believe that, okay, this guy must be a special episode only character. But then the episode ends and he doesn't die or decides to stay somewhere else, he gets back to the TARDIS with the Doctor.
And when season 4 really starts he's still there. He's not replacing Donna though, she's still there and, in fact, this guy gets along amazingly with Donna, they're both witty and sharp and, more than anything, looooove bullying the Doctor (with love). And as the season moves forward it is more and more obvious that this guy has a massive crush on the Doctor, doing more and wilder things on their adventures to try to impress him, and by the way the Doctor worries after him it is also clear this is not one sided, they're just dumb and bad at communicating, in fact we get some funny little episode of Donna trying to play matchmaker.
And everything is good and fun and normal until the Daleks get involved by the end of the season and then we start getting time war flashbacks and it's clear the intention is for us to assume they're from the Doctor and as it keeps advancing we see on the memories how this person burns worlds and kills people and it's meant to shock the viewer about what kind of person was the Doctor during the war.
And there would be no meta-crisis, the Doctor doesn't get shot running to Rose.
Instead of Donna being trapped in the TARDIS when it's chucked to the heart of the Dalek ship, it's this other companion and as he and the TARDIS are plummeting to their deaths, the TARDIS opens a secret compartment on the console and that's where we cut to black and to the Doctor who is absolutely destroyed at thinking his companion is dead and the TARDIS is gone and Donna is crying and things go on with Davros plan until the TARDIS appears again and the door blasts open with music loudly from the inside and the Doctor has a look that it's equal parts relief and dread.
This guy turns up and starts shooting daleks with a weapon no one knows where he got from but it's working so they're not complaining and then he starts messing with that machine that controls the Daleks and the Doctor is running to help him but the Doctor is not looking at him no matter how insistently this guy is looking at the Doctor and as he gets more annoyed that the Doctor is not looking back he decides to blow up all the Daleks. And that's the first time the Doctor does look at him and they lock eyes and everything is exploding around them but they're just looking at each other until the others grab at them to run to the TARDIS, which they do and they start flying it together which Donna is the only one that finds it strange because she knows the Doctor never taught either of them to fly the TARDIS but this guy is doing it like he's an expert and even correcting things the Doctor is doing.
They don't talk again while everything is winding down and they're dropping everyone home and then they appear on Donna's house and the Doctor is like "go check on your family, I'll be back, we're just going to check on his family too"
And then they're alone and there's just silence as the TARDIS goes into orbit. And then the Doctor calls him Master.
Then we get a flashback to the ending of season 3 where we see that hidden on the way the Doctor was cradling the Master's "body", there was the glow of regeneration. We see how after the season ended and the Doctor went on his way, he went into the infirmary and saw the unconscious Master that had regenerated into what we thought was his new companion and we see him grapple with the idea of what to do now and then he uses the chameleon ark on the Master and when he wakes up, he thinks he's human and the Doctor's companion who got hurt on an adventure and that's why he's in the infirmary, he says he feels fine and it transitions to them flying the TARDIS on the first scene of the space Titanic special. It's also made clear that all the time war flashbacks we saw before were the Master's, not the Doctor's.
They argue over how fucked up the Doctor's morals really are below his facade of being a hero, of how he did that and now the Master is grappling with never being himself in this body before and he's so angry and they fight, physically, and the Master kills the Doctor, who regenerates into Eleven and they're crashing on Amelia's backyard.
And they're still arguing as they come out of the TARDIS and meet her and because the Master knows how to fly the TARDIS better and he's not going through post-regeneration, they are back in five minutes and end up kind of adopting Amelia together before they ever manage to go back to Donna.
So when do go back for her, her bestie turned out to be a Time Lord, the Doctor has a different face and they have a child. This is a wild day for Donna.
And because the boys can have no rest, the Naismith people are coming for them and they manage to trap Amelia to force the Master and the Doctor to cooperate and, somehow, Donna is going to save the day and no one is going to die (again) and no one is getting dragged to Gallifrey.
The group is still together for season 5, where they gotta deal with the cracks in the universe but that season would be wildly different since Amelia is a child, not an adult, and we don't really have Rory or River
That's all I have for now. If I get a more clear idea of what season 5 and further would look like, I'll probably add to this but who knows. I just really like the idea of the Doctor being as unwell and toxic about the Master as the Master is about the Doctor.
