I'm surprised that is this the first episode to air, as well as to be filmed. I thought I read somewhere that the first episode to be aired is usually filmed maybe 3rd or 4th in the shooting schedule? The reason being, it gives the actor time to settle into the role; if he's still finding his feet in his first full episode, it might leave a bad first impression with viewers. And you know what they say about first impressions? But Capaldi is in Matt Smith's outfit, so I guess this is set immediately after TOTD.