This machine was considered an marvel of the ancient and lost technology created by Mankind. It was believed to had been more than ten thousand years old by M41 and dated to the times of the Emperor during the years prior to the betrayal of the Warmaster Horus. In this time, it was said in holy tomes that spoke of "His Works" which were his hidden secret machinations within the laboratoria beneath the Imperial Palace on Terra. The arefact drew on the power of the Empyrean and seemingly required a psyker of sufficient power to activate the device. It was believed that the ultimate purpose of this engine was to help in the transformation of Mankind into a powerful psychic race. Eventually, it was left behind on the planet Neva where it was placed within the protected region of the Null Keep with only the Gethsemenite religious sect being aware of the location of the psi-engine. After the Horus Heresy, its existence was seemingly forgotten by the greater masses of the Imperium of Man.
Within the forbidden tomes remained the knowledge of the engine which was retained in the old creed and was one that the Adeptus Ministorum considered apocryphal. This meant that later generations of the Ecclesiarchy considered them to be heretical with none daring to speak of them as their contents included mention of star-children and the births of new gods. Discovery of such information meant that any such heretics would be punished with the death sentence. At some point, Viktor LaHayn of the Ecclesiarchy began to read through the ancient forbidden tomes and learnt of the existence of the engine on Neva. This brought him into contact with the Gethsemenites and he was eventually taken to the engine by one of the sects abbot's who put a blindfold on him until he was escorted to the machine located in the Null Keep. Once there, LaHayn believed himself to be the chosen being who could use the device to ascend into a being as powerful as Malcador the Sigilite whereupon he would awaken the Emperor who was trapped within the Golden Throne. To protect the secret of the Psi-Engine, LaHayn had the abbot and all the Gethsemenites eliminated by his psyker prodigy Torris Vaun.
As part of his plans to bring the device operational, Viktor LaHayn had a number of Techpriests brought into his forces. These individuals were either kidnapped or subverted to his cause where they initially protested or demanded to be set free as they claimed to be devoted servants of the Machine God. This was the case initially until they witnessed the engine whereupon they decided to break their oaths to the Adeptus Mechanicus in order to willingly serve the LaHayn. According to him, this was because they recognised the machine to be one of the greatworks of the Emperor. During this time, its known that these tech adepts attempted to explain the science behind it to him though the Deacon was content to know that it was a creation of the God-Emperor. Its importance meant that the Deacon LaHayn tended to spend much of his time in the engine chamber which contained the machine within the Null Keep. After freeing himself, Viktor LaHayn's enforcer Vaun decided to subvert the machine for his own purposes namely to bring about anarchy and disorder.
Vaun eventually orchestrated a riot amongst the psyker prisoners of LaHayn within the Null Keep in order to reach the psi-engine and even entered into the machine. However, he was unaware that it required a psychic ignition spark to activate and thus became the unwitting and unwilling subject to initiate the artefact. Once activated, he attempted to resist its influence but the Deacon LaHayn killed Vaun thus leading to his body being absorbed into the engine. This allowed LaHayn to be transformed into a psychic being and he attempted to convert Sister Miriya and her squad of the Adepta Sororitas to his goal but they refused. Ultimately, Viktor LaHayn was killed in the struggle as he was unaccustomed to such powerful psychic abilities and the engine fell into the magma core of Neva. His death led to a destabilization within the psi-engine that weakened the barriers to the Immaterium and an orbital strike led to the destruction of the site of the Null Keep thus leading to the Emperor's lost engine being destroyed.
The engine itself was noted as being as large as a house though it floated over the floor with nothing holding it up except for an azure glow. In appearance, this machine contained two great spinning rings of black steel that constantly turned about the construct's central axis and spun like coins about the engine. The slow orbit and motion of the rings as the metallic rods within them tended to have a hypnotic effect on viewers who felt light-headed after staring at them. Their components worked with one another without touching or connecting with themselves in anyway whilst an energy field was generated by the device which created a nimbus around it. Numerous levers and dials were located on parts of the machine that were able to shift the huge mass of the engine. In addition, it seemingly fed on the power of magma located below Neva.
When not activated, the simple touch of the energy of the machine produced by the spinning machines sent trickles of force into an individual where they felt the merest fraction of the true potential energy of the engine. Even in this state, the primitive brain of such a being struggled to comprehend the power of the machine and sensed something much greater beyond their reach. When activated, the great circling rings hurled at one another in defiance of gravity with thunderous roars of white energy emerging about the machine. Within the coils of blue energy were texts in High Gothic that emerged on the faces of the rings which detached themselves to float in the surrounding air. As the machine built up, a rumbling pulse emerged within the shifting planes of metal that were contained at the core of the engine. As the metal planes shifted, the spinning rings eventually merged with an object coalescing from within the engine that took the form of an iron throne. This extended from the engine on a spinning glow rod of brilliant white that was awash with energy.
To initiate the psi-engine, a powerful psyker was required to sit within the machine though typically this needed to be a willing subject. This was because an unwilling participant could bring about sympathetic feedback into the machine which created great flames of psy-fire from the rings that could spread about the black stone chamber containing the artefact. This was because of great psychic energies of impossible power charging the flesh of any occupant within psychic potential beyond comprehension. This was because the spinning rings slowly formed a conduit into warp space as it began to absorb its psyker occupant. This allowed the psi-engine to transform non-psykers into powerful psychic beings. It was believed by LaHayn that the engine had the power to remake the stars and turn its users into a god.
The novel gives multiple names to the machine with it commonly referred to as the "engine" though a second reference is made to it being called a "psi-engine".