The Order of the Gray Knights has specialized in exorcising demons since ancient times and works closely with the Inquisition. Ten centuries ago, on the planet Corion IX, the Gray Knight Mandulis fought against the demon Gargatuloth. In a battle that cost him his life, Mandulis still managed to expel the creature back into the Immaterium. A thousand years later, the renegade inquisitor again opens the way to real space for the demon. Justice Alaric, commander of an elite squad of Gray Knights, must discover and destroy the cult that is plotting the return of a powerful demon. But time is running out, it is no longer possible to prevent the appearance of Gargatuloth and we must find a way to drive him into the underworld again...