Parts: 1 (50-minute)
Writer: Steven Moffat
Airdate: 15 April 2017
Production Code: n/a

Doctor: twelfth
Companion: Bill, Nardole

Creature Feature: Daleks, Movellans

Story: Summoned to the office of a university professor known only as the Doctor, Bill Potts - not a student, but a server in the canteen - learns that she's been spotted attending his lectures, and the Doctor has taken an interest in her academic success. Without the university's knowledge, the Doctor takes Bill as his private tutee, educating her in physics and astrophysics, at which Bill discovers she excels.

So when her would-be girlfriend begins acting strangely, and shows Bill a mysterious puddle in which her reflection is inexplicably wrong, Bill confides in the Doctor... who, despite his best efforts, pulls her headlong into a sci-fi world that Bill thought only existed in the movies.