The physical world existed alongside a concentration of pain and fear that Dr Colin Dove believed was the manifestation of real evil. Some places, termed leprous houses by the Bible, acted as synapses between this force and the physical world. Dr Dove termed it a "reservoir of evil" or a "reservoir of pain".
This force existed on a higher plane and went undetected by most, although sensitives were able to sense it to varying degrees. At synapses, the force could influence and even control sensitives, causing them to commit murder and granting them some supernatural powers such as astral projection. The two worlds were closest at perihelion in August.
On 13 August, 1945, the force possessed young Daniel O'Kane and had him murder his mother, father and sisters. Daniel was the most sensitive person known to Dr Dove until Peter Russell. Dr Dove, somewhat sensitive himself, wished to unleash the force in 1994 using Daniel and Russell at perihelion. He became obsessed with learning what would happen if this came to pass.
By August 1994, the force had killed nine people through Daniel before killing William Bruffin, who they reanimated briefly. Dr Dove saw this as a sign that it was almost perihelion and time for Daniel and Russell to meet. The force killed Dr Dove when he was no longer of use and was breaking through before Daniel, in a moment of clarity, jumped in front of Russell's blade and saved Dr Liz Shaw. Daniel's death meant that the force could not be unleashed.
The force still had a connection to the physical world, however, as shown through a psychic connection between Russell and Patient One. (HOMEVID: The Zero Imperative) In the early 21st century, P.R.o.B.e., under Giles's leadership, awaited another perihelion. (WC: Shadows of Doubt)