While trapped in the dog dimension, the Thirteenth Doctor wrote a book which she managed to send back through to N-Space.
The book was intended to help whoever found it learn to fill the shoes of the Doctor, protector of the universe, until the real Doctor could find her way back. It also included an introduction by the Doctor and brief profiles of herself and her companions. The Doctor's symbol marked out specific passages wherein which the Doctor had appended "hints and tips" to the challenges laid out by the book. (PROSE: Meet the Fam)
In her book, the Doctor included fact files on her latest adventures, (PROSE: Fact File) reviews of recent destinations she has visited, (PROSE: TARDIS Trip Reviewer) a tour of her TARDIS control room, (PROSE: TARDIS Tour) her own write up on legends of the Timeless Child, (PROSE: The Secret of the Timeless Child) and an extract from the The Dark Times Times newspaper article about the Dark Times, written by River Song. (PROSE: The Guide to the Dark Times)
Behind the scenes
- The metafictional implication is that the book written by the Thirteenth Doctor is none other than Doctor Who The Official Annual 2021 itself, with the challenges preparing the reader to become an "interim Doctor" being the games and activities contained in the book on top of various prose stories.