The Sound of Drums. Said Timelord (who's evil and calls himself the Master) is the Prime Minister of England (I'd assume after Harriet Jones resigned, because I don't think she could have finished her term...) and Martha's family is all kidnapped. So then this plan the Master has sort of comes out, cuz there are these little metal ball things that look like the Oracle from Halo who want him to do something (presumably take over earth for them). And...everyone goes up in this huge Avengers-esque ship in the sky, and the Doctor gets captured by the Master, and made old...honestly, I'm just going to overlap into the final episode, because I'm not sure where the gap is...So yes, the Doctor is made old in varying stages. First he's just made like 100 or something, but then the second time, he's made 903, the Doctor's actual age. And he's super tiny now. Anyways, Martha escapes and goes around the world, to help set up a plan the Doctor came up with. Oh, and Jack is also captured, but no one cares cuz he can't die. So then Martha gets captured, and the Master tries to execute his plan, but then the Doctor's plan triggers, and every single person in the world (a number that is smaller, by the way--oh, and the TARDIS is being transformed into a paradox, which is significant, but I never really understood it so whatevs) thinks the words "the Doctor" and creates a telepathic field that saves the Doctor and makes him young again, and then the Master is defeated, and then he gets shot, and the Doctor tries to get him to regenerate, but the Master is smart, and doesn't. Just to hurt the Doctor, he decides to die. I thought that was brilliant (sad, but brilliant). So then, as far as we know, the Doctor is, again, the last Timelord. The paradox in the TARDIS does something, and everything goes back to where it was before the whole Master thing happened. So the world isn't half in ruins, and the Master isn't the Prime Minister, but the elections are going on. So, yes.
Martha decides to stay behind and do her medical stuff to become a doctor. Then Jack is musing about his inability to die, and if that means he'll live forever. Maybe he'll live millions of years. And what'll he look like. The Doctor says he can't know.
Jack: Ok, vanity, sorry. Yeah... can't help it. Used to be a poster boy when I was a kid, living in the Bo-shang peninsula... tiny little place. I was the first one ever to be signed up for the Time Agency, they were so proud of me. The Face of Bo they called me... hummm! I'll see you! [Author's note: thanks to IMDb for this quote!]
So...Captain Jack is the Face of Bo. That's freaking crazy! We all sort of freaked out (as, indeed, did the Doctor and Martha haha) That was a fun ending. So, going into the Christmas special, the TARDIS crashes into the Titanic. I love this show.