Kate Lethbridge-Stewart responds to a message from ex-UNIT operative Douglas Cavendish to investigate a haunting.
Arriving at Cavendish's isolated cottage, she faces a demonic power her father had previously battled. Summoned by a future tyranny, a Dæmon is set to return to Earth. It is up to Kate and Cavendish to save the planet and its future.
Kate has heard enough stories of UNIT to not simply dismiss Cavendish's claims out of hand, but is still surprised and dubious, implying that she has not yet begun her UNIT career. This is further implied by the fact that she has not yet dropped "Lethbridge-" from her name.
Cavendish refers to UNIT having a top secret storehouse of alien technology in the suburbs of London, and that it contained crates of shop-window mannequins (i.e., Autons). The warehouse and its crated Autons were depicted in 1997's Auton. The warehouse would be later identified as the "Black Archive" and depicted in Enemy of the Bane before being relocated under the Tower of London before the events of "The Day of the Doctor".
Among the UNIT relics which Kate finds in Cavendish's garden shed is a Cyberman breastplate.
Kate is physically duplicated in an attempt to dupe Cavendish. She is again duplicated in "The Day of the Doctor".
Kate refers to her son, Gordon / "Gordy", who was introduced in Downtime, and whom Kate gave her father's middle name.
In the repeated mentions of Kate's father - including a recitation of his post-nominals by Cavendish—his eventual knighthood is never referred to, implying that he was created Sir Alistair sometime after this story.
A close-up of a x-ed off calendar and Cavendish's exposition reveal the dates of the story as 30 and 31 October 2003.