"Sandmen" was the name given by Clara Oswald and the Twelfth Doctor to a carnivorous form of life created in the 38th century by human sleep dust after sleeping in a Morpheus pod. The pod changed the fundamental chemistry of the brain by sending a coded electronic signal to certain parts of it. The Sandmen could break apart into piles of sleep dust that were also released into the air that could gather information. The sandmen were also blind and relied on their hearing to hunt and consume their prey. The Sandmen absorbed their victims by reaching out branches of sleep dust to drag them into the Sandman itself.
The Sandmen attacked the Le Verrier space station, and later killed the rescue team members Deep-Ando, 474 and Chopra, while they were looking for Gagan Rassmussen, Morpheus' inventor. Rassmussen released the supposed original Sandman, dubbed "Patient Zero", from its pod. They were defeated when the Twelfth Doctor destroyed the space station's gravity shields, and the Doctor and Clara Oswald planned to destroy any remaining Morpheus pods to stop any more Sandmen. However, as part of a show for dramatic effect, Rassmussen, who at this point had become a Sandman himself, sent a video of the adventure containing a message encoded with the same signal in Morpheus pods that could create further Sandmen out of the sleep dust in humans' eyes throughout the solar system. (TV: Sleep No More)