The Doctor and Ace are locked up. The TARDIS is gone. Things just couldn't get worse, could they?
Of course they could. Things can always get worse — the new President of the Solar System, Josiah W Dogbolter, didn't get where he is in life without learning that. That's why he has a Quantum Possibility Engine. It's a wonderful machine, creating a wonderful Solar System. And with this wonderful device, he can bring happiness and peace to all.
Either that or tear the universe to shreds, it's hard to be sure which.