Doctor: Peter Capaldi (Twelfth Doctor)
Companion: Jenna Coleman (Clara Oswald)
Reece Shearsmith – Rassmussen
Elaine Tan – Nagata
Neet Mohan – Chopra
Bethany Black – 474
Paul Courtenay Hyu – Deep-Ando
Paul Davis – King Sandman
Tom Wilton – Sandman
Matthew Doman – Sandman
Zina Badran – Morpheus Presenter
Natasha Patel – Hologram Singer
Elizabeth Chong – Hologram Singer
Nikkita Chadha – Hologram Singer
Gracie Lai – Hologram Singer
Nikki Wilson – Voice of the computer (uncredited)
Directed by Justin Molotnikov
Written by Mark Gatiss
Script editor David P Davis
Produced by Nikki Wilson
Executive producer(s) Steven Moffat
Incidental music composer Murray Gold
Series Series 9
Length 45 minutes
Originally broadcast 14 November 2015
The viewer is addressed by Gagan Rassmussen, a researcher aboard the Le Verrier Space Station in orbit around Neptune in the 38th century, through a glitch-filled video. Rassmussen warns the viewer not to watch the video, but says its found footage will explain the events that have transpired.
Hours earlier, a rescue ship is dispatched from Triton when communication with Le Verrier is lost. Aboard, the four soldiers, Nagata, Chopra, Deep-Ando, and 474, discover the station empty save for the Doctor and Clara, passing off as assessors. The group is chased by "Sandmen", humanoid forms composed of dust that are impervious to weapons.
They take safety in a lab filled with large pods, and discover Rassmussen. He explains they were testing the next iteration of Morpheus, a device that uses electrical impulses to the brain to compress a month's worth of sleep into a few minutes, when the Sandmen appeared and devoured the rest of the crew. Chopra notes that Morpheus is controversial and has refused to use it. The Doctor suspects that Morpheus and the Sandmen are connected, the latter formed from rheum. Sandmen flood the room and appear to consume Rassmussen; the others escape when a fluctuation in the station's gravity shielding temporarily disintegrates the Sandmen.
Chopra, Deep-Ando, and 474 are killed during their escape. In safety, the Doctor monitors the Sandmen and realises they are blind and are receiving some type of video signal, which he views through his sonic sunglasses. The video shows the various points-of-view of all but Chopra, and the Doctor confirms the Sandmen are being controlled by the Morpheus signal.
They make their way to the ship but Rassmussen is alive, trapping them in a room with a Sandman. Rassmussen plans to use the ship to return to Triton and release Morpheus there. The Doctor engineers their escape and forces the gravity shielding to fail, sending the station and ship into Neptune. The Doctor comments that the situation seems too contrived for them to have been in any real danger before they leave in the TARDIS.
Aboard the ship, Rassmussen reveals to the viewer he is also a Sandman, being affected by the gravity well. Before disintegrating, Rassmussen explains he wanted to assure the video the viewer is watching was seen by others, as its glitches contain the Morpheus signal and will allow it to spread.