The source of magic in the setting is a parallel universe of supernatural energy known as "the Warp". All living creatures have a link to this place, but certain individuals called "psykers" have an especially strong link and can manipulate the Warp's energy to work magic. Psykers are generally feared and mistrusted by humans. Psykers can possess many dangerous abilities such as mind control, clairvoyance, and pyrokinesis. Moreover, the Warp is full of predatory creatures who might use a psyker as a conduit by which to invade realspace. However, psykers perform critical services for humanity: their powers permit faster-than-light communication, which is impossible under the "normal" laws of physics, and on the battlefield they counter the powers of enemy psykers. A key theme of the setting is that for all the problems that psykers pose, human civilisation cannot do without them. For this reason, psykers must be trained to control their abilities and resist Warp predators. Those who fail or reject this training are executed for the safety of all. Those who pass their training are pressed into life-long servitude to the state and are closely monitored for misconduct and spiritual corruption.