The Doctor and another time traveler (the master?) were talking to each other about who went back in time earlier and set up or undid traps for the other one, over several iterations
things like : Well I went back in time further before you set up that trap and undid it and placed my own
I knew you’d do that so I went even futher… etc etc
It may be a Parody but its a lovingly made parody thats as good if not better than most of Dr Who, modern or classic.
And it’s the first Moffat episode.