A Mystic is a minor Imperial psyker, chosen for his or her unyielding willpower and utter reliability in the face of daemonic temptation. Though a Mystic lacks the mental fortitude to summon the destructive fury wielded by other psykers, he can nonetheless conjure a steady psychic signal. Though weaker, this signal is not dissimilar in nature to that projected by the Astronomican, and can be used as a beacon for troops answering an Inquisitor's summons. Many Inquisitors maintain whole choirs of mystics on the Imperium's far-flung worlds, the better to coordinate the completion of their plans and reinforcement of their armies. So have the Mystics proven crucial to many an Inquisitor's designs.
- Codex: Inquisition (6th Edition), pg. 87-88