Great instinct! As we’re sure you noticed, the bucket of cleaning supplies that was so essential to your escape from the locked room at the beginning of our adventure wasn’t in the building when you went back in time. So who put it there?
Why, you of course! The bucket was there because you’d already saved the world and gone back in time to put it there, as you’re about to do now. CLASSIC Bootstrap Paradox, eh?
And with the bucket there, all the loose ends are tied up and the danger has all passed. You’ve saved the world, defeated the Dalek and got away scott-free, and that means you’ve won our game!
Congratulations – the Doctor himself couldn’t have done any better.