Forest of the Dead
In the episode, the time-travelling temp Donna Noble is trapped inside a virtual reality in a planet-sized library's hard drive in the 51st century and has false memories implanted of a married life.
The Tenth Doctor, River, Strackman Lux, and the remainder of their team flee the microscopic Vashta Nerada on the planet-sized Library.
The Doctor realises Charlotte's mind is struggling to cope after "saving" the thousands of patrons by transferring their physical forms to the computer core 100 years ago when the Vashta Nerada attacked.
Within the simulation of a contemporary Earth village, Donna is tended to by Dr Moon (an avatar of the virus checker program) and introduced to Lee, whom she marries.
Aware that time seems to be skipping, Donna is alerted by Miss Evangelista, one of River's team members killed by the Vashta Nerada, that she is in a simulation.
The Vashta Nerada allow the Doctor one day to free the people trapped in the computer core, including Donna, after which the Library will belong to them.
River knocks him out and takes his place, insisting that the Doctor's death now would prevent her meeting him in her own past (due to their mismatched timelines).
[7] Kingston was not told her role was supposed to be recurring, learning only later that Moffat always intended for Song to come back for return appearances.
[13] Various new locations were also used for this episode; the climactic scenes of the episode, in the library's computer core, were filmed in an electrical substation of a disused Alcoa factory in Waunarlwydd, Swansea,[14] scenes set in CAL's databanks were filmed at Dyffryn Gardens, St Nicholas;[15] and outside shots were shot across Wales in location such as Palace Road, Victoria Park and Hensol Castle.
[24] Similarly, Patrick Mulkern of Radio Times found River Song to be an interesting character, and liked the "reams of brilliant ideas" in the episode.
[25] Simon Brew of Den of Geek heavily praised the episode for its "complete" utilisation of characters and its "masterful" scripting.
[21] Ben Rawson-Jones from Digital Spy found that the episode used psychological fears to "brilliantly build" upon the opening; and praised the "stunning twist" on the concept of the parallel world.
[26] Radio Times named the two-parter Moffat's ninth best story, praising the "spectacular" cast, and calling the script "deliciously creepy" tying everything together.
[22] This episode, along with "Silence in the Library", was nominated for a Hugo Award in the Best Dramatic Presentation, Short Form category, but lost out to Dr. Horrible's Sing-Along Blog.
