Demigest was a planet colonised by humans in the early years of their travels through space.
Space and time never existed in an established order on Demigest. The Eighth Doctor claimed that primal universal forces existed on the planet, which soaked deep into the planet's bones. (PROSE: The Infinity Race)
The original colonists to Demigest were infected by the primal universal forces on the planet, giving them supernatural powers. The colonists then began to refer to themselves as the Warlocks of Demigest.
Shortly after Earth lost contact with Demigest, a second ship was sent out to the colony. A single survivor of the second expedition, Trudeau, fled the planet in an escape pod, knowing that he couldn't survive but desperate to warn Earth of what he had found. He recorded an oral log, which was later transcribed into a book, The Black Book of Demigest.
Sabbath came to Demigest and kidnapped two of the Warlocks for his plans on Selonart. Failing in these plans, the Warlocks captured Sabbath and took him back to Demigest. The Doctor arrived later to free Sabbath, killing the Warlocks in the process by unleashing the primal universal forces found on Selonart. (PROSE: The Infinity Race)