Smile (in-universe)

The first two episodes of a new series of Doctor Who had been broadcast by the time a letter from the Twelfth Doctor had been published in an issue of Doctor Who Adventures. They featured the first appearance of the Doctor's then-newest companion, Bill Potts. (PROSE: Dear Readers)

The Twelfth Doctor, Bill and Nardole strolled past books with the titles The Pilot, Smile, Thin Ice, Knock Knock and Oxygen in a library. (TV: A Time For Heroes)