A tonne of foreshadowing and a very common courtesy unit, plus the very first appearance of Professor River Song (on our timeline)
The Doctor and Donna are summoned via Psychic Paper to The Library, a planet-wide library in the distant future, full of actual, bound, printed-on-paper books, but oddly devoid of people.
Meanwhile a mysterious young girl in present-day England, with inexplicable visions of the library, and of the Doctor and Donna, is being interviewed by the equally enigmatic Dr Moon.
Cut back to the library, where an old friend of The Doctor’s whom he hasn’t met yet, Professor River Song, is leading an expedition for the Felman Lux corporation, and where an alien force appears to have taken over.
This is part one of the magnificent Steven Moffat two-parter comprising Silence in the Library and Forest of the Dead.
Oh, and check out this neat teaser we put together moments before pressing record, because why not?