|This page contains spoilers for:||Faith and Fire (Novel)|
Powerful, charismatic, and possessed of a hunger for arcane knowledge, LaHayn was approached by a sect of Gethsemanite monks who led him to a fortress called the Null Keep on Neva's surface, at the center of which was a "psychic engine", which they believed had been created by the Emperor himself.
The discovery of this device, coupled with scraps of ancient documents declared heretical by the Ecclesiarchy, would set LaHayn on an obsessive quest to fulfill what he believed was the Emperor's ultimate purpose. Noting that more humans were being born with psychic ability with each passing millennium, LaHayn believed that mankind was evolving towards becoming a race of psykers, and that the Emperor had been trying to engineer just this result during the last days of the Great Crusade, before he was crippled by Horus. Since the Horus Heresy, LaHayn believed, mankind had been stifling its own destiny by treating psykers as aberrations to be feared and hated, despite the vital role played by astropaths and Navigators in the daily running of the Imperium.
LaHayn consolidated his power on Neva by recruiting rogue psykers from Neva's population to serve as test subjects inside the Null Keep, and as his personal henchmen to eliminate his opponents in the Ecclesiarchy and the planetary government. He also had the Gethsemanite monks hunted down and killed, to keep the Keep's existence a secret.
LaHayn intended to use the psychic engine to make himself into the most powerful psyker in the Imperium, the "Second Sigillite" and successor to Malcador. He believed that if he could become powerful enough, he could resurrect the Emperor from his imprisonment on the Golden Throne and allow the Father of Mankind to walk amongst his subjects again.
One of the keys in his scheme was Torris Vaun, a dangerously powerful pyrokene that LaHayn had recruited as a young child and used as an assassin before Vaun went rogue. LaHayn lured Vaun back to Neva and tricked him into entering the psychic engine, using him as the "spark" that would ignite the engine. Vaun was eventually consumed by the ignition process, while LaHayn was imbued with nascent psychic powers.
Confronted by Sister Miriya of the Order of Our Martyred Lady and Sister Verity of the Ordos Hospitaller, LaHayn invited them to stand with him in fulfilling mankind's destiny. They refused, and Miriya attacked him. At first, LaHayn's powers were enough to deflect the shots from her plasma pistol, but Miriya waited until the gun overloaded, then threw it into LaHayn's arms. The weapon's detonation, combined with the raw psychic energies unleashed, boiled LaHayn's body away to nothing. The Null Keep was flattened by the Imperial Navy shortly thereafter.
In the aftermath of the whole sordid affair, when Canoness Galatea was threatening Miriya with execution for disobeying her orders, Verity stepped forward and said that faith is only worth having when it has been tested against the unexpected and the impossible, and still holds strong; LaHayn fell into heresy through his dogged belief that what he was doing was right, despite any opinion or evidence to the contrary, but Miriya did not make that mistake. The Canoness was impressed, and mitigated Miriya's punishment to demotion to ordinary line duties.[1x]