The Twelfth Doctor and Clara Oswald owned a book which contained a record of their adventures together and of the variety of "monsters" who had tried to invade the Earth at one time or another.
Clara once hid nine of the Doctor's TARDIS keys inside its pages. The Doctor, at any rate, feared what might happen if ordinary 21st century humans got their hands on the book, and left a series of post-it notes on its first pages, urging any stranger who'd picked it up not to read any further. (PROSE: I'm The Doctor!)
Behind the scenes[]
Doctor Who The Official Annual 2016, implied to be the very book mentioned by the Doctor.
- The metafictional implication is that the book written by the Twelfth Doctor is none other than Doctor Who The Official Annual 2016 itself.