The Le Verrier was a space station orbiting Neptune in the 38th century. It had a security system where doors would only unlock if those wishing to enter the locked room sung the song "Mr. Sandman" by the Chordettes.
Professor Gagan Rassmussen invented the Morpheus pod on the space station in the 38th century. Sometime after this event, the sleep dust on the eyes of the people who used Morpheus turned into the Sandmen, which completely enveloped the crew and transformed them into creatures of their own kind. Rassmussen, at this point a Sandman, devised a plot to spread the Sandmen throughout the solar system, by using the same encoded signal inside Morpheus that created Sandmen out of the sleep dust. He did this by orchestrating a scenario filled with plot twists and a climax on board for dramatic effect "like a story", and send a video of this story with the signal.
The footage that Rassmussen recorded was later used in the episode of Doctor Who entitled Sleep No More, which was broadcast in late 2015, and was available on BBC iPlayer by 2020. (WC: The Zygon Isolation)