Cauchemar was a human geneticist who was exiled to a prison colony on the New Earth frontier. His crime was experimenting on fellow colony members in a quest for immortality. Although his efforts made his cells capable of dividing almost endlessly, they mutated.
As Cauchemar was being taken to prison, his ship was damaged and some of the prisoners took over certain functions to keep the ship going. Cauchemar fell in love with his warden, Jasmine, in the process, but she could never love him knowing what she did about his past. The ship passed through a spatial anomaly that damaged the cells of the crew. They were contacted by beings of pure energy who had elevated themselves to this level of existence after discovering the gene for the soul. They wished to dispose of their criminal element. Cauchemar engineered the humans into carriers, living prison cells for the aliens' criminal souls, but created a symbiotic relationship so the human souls would share in the testing and be able to achieve communion with the Universe, monitored by the Holiest, beings genetically engineered from the dead to pass the judgment of the "Creator", the controlling program.
However, Cauchemar's experiments upon himself had rendered him unsuitable as a host and the aliens' offer of freedom was no longer enough without Jasmine. Cauchemar was expelled from the world, but found his way back and became involved with the "reincarnation" of Jasmine, even though he knew that his intervention — and, indeed, his eventual offspring — would taint the gene pool, creating humans who went around with nothing but their own baggage, rather than a recreated soul getting another shot at life. Cauchemar's transition through space had also left him fatally ill, causing his immortal DNA to collapse in piles of sludge. When he tried to save himself by taking genetic samples from "Jasmine", she was badly injured. He tried to take her to the water mountains where the Creator existed, hoping that the Creator would aid him for making this world possible, but the Creator could not perceive Cauchemar and its defences unmade Jasmine's DNA. His closeness to Jasmine allowed Cauchemar a moment of bliss as her entire life was made known to her.
Cauchemar wished for the chance to know himself. He built devices with stolen genetic equipment to save himself. All they did was put off his own inevitable death, even as he refused to let the world he had created go on without him. Taking advantage of the fact that the Creator could only detect the colonists containing the godswitch on chromosome 13, Cauchemar lobotomised colonists. He removed the aliens' essence to make them invisible to the Creator. Served by these, he searched for years for the colonist who reincarnated Jasmine.
Finally, Cauchemar — now calling himself Derran Sherat — believed he had found Jasmine's soul in a woman called Treena Grace. He had a child with her after he also had a son with Treena's sister, Ettianne. To force the Creator to accept him, Cauchemar genetically engineered a baby with the fingers of colonists he had murdered. As their flesh still lived in the baby, their godswitches — the DNA that let them know the meaning of their lives — were never thrown. He intended to kill the baby close to the Creator. This would release the built-up potential energy of all the experiences within it, disorientating the Creator. He would further overwhelm it by murdering the inhabitants of the planet's sole city with a network of bombs. The resultant self-defensive frenzy of the Creator would cause a feedback of energy into the remaining colonists, killing everyone carrying the godswitch, and preventing any more of the alien souls being released, while Cauchemar killed Jasmine's current host and rode into Heaven with her.
Treena discovered his plan and was disgusted by it. Cauchemar concluded that her lack of understanding "proved" she couldn't be Jasmine. He allowed her to die during a botched bank robbery when she tried to kill him. He turned his attention to Ettianne — who guarded the "mooncalves", individuals lacking a godswitch and born deformed due to Cauchemar's past interference in the planet's development. He sent his agents to collect her. They failed when the Doctor, Fitz and Anji arrived on the planet by chance and interrupted the abduction.
Aided by Nathaniel Dark, one of the Diviners — people who worked out the meaning of peoples' lives when they didn't die natural deaths — the Doctor concluded Derran Sherat was the key to the puzzle. It was too late to stop Cauchemar's agents capturing Ettianne's son Braga to force her to come to him. The Doctor took Ettianne's place. He confronted Cauchemar and recovered Braga after learning his true history, but Ettianne was captured by Cauchemar during their escape and taken to the Creator's mountains.
The Doctor realised Cauchemar had "named" his followers according to grids and locations on the city's map. He deduced that the people were named for the places they would set off their bombs in the final attack on the Creator. As one of the men had been killed during Ettianne's capture, he thought that Cauchemar's right-hand-man, Hox, would take his place. The Doctor dispatched Fitz, Anji and Dark to stop Hox while he and the mooncalves went to save Etty. In the confrontation, Hox was killed, destroying Cauchemar's plan — his followers could not set the bombs off themselves. The infant was killed while the mooncalves got Etty to safety. As Cauchemar's body finally fell apart, he tried to kill the Doctor by dragging him into the water with him, but, as Cauchemar died, the Doctor put himself into a healing coma, allowing his body to drift until Fitz and Anji could recover him. (PROSE: Vanishing Point)