We watch "Mummy on the Orient Express" (Series 8, Episode 8) where the Doctor takes Clara on one last adventure since she’s vowed to Danny that she’s done with time travel. For reals! (Wink) So they hop on the titular space-train loaded with extras from a somewhat less racist Agatha Christie novel. (As if...) Whilst enjoying their 'last hurrah' mysterious deaths occur at regular intervals, the Doctor finally gets to see his Mummy, and Clara lies real good to Danny cuz she ain’t quitting. Good thing there’s no Unbreakable Vow in this Whoniverse.