"Ego, Draco Ordinis Mallei Inquisitor, per auctoritate Digamma Decimatio Duodecies, ultimum exterminatum planetae Stalinvastae cum extrema celeritate impero."
Stalinvast was once a rich and thriving Hive World covered in coral-like city growths, between which grew vast blue-green jungles filled with teeming life and vicious predators. It was used in the manufacturing of weapons for the Imperium of Man, and became the site of a Genestealer-instigated rebellion against the Imperium in the early 39th Millennium. The planet was later the target of a falsified Exterminatus Order, and was subsequently reclassified as a Dead World.
The Genestealer-lead rebellion on Stalinvast was ultimately extinguished by the Inquisitor Harq Obispal, his retinue of Acolytes, and the troops of the Stalinvasti Planetary Defence Force, with excess force and raw suppression, resulting in possibly millions of unnecessary civilian deaths. Obispal was also a member of the secret Inquisitorial conspiracy known as the Ordo Hydra, and the excessive zeal he had displayed in quelling the rebellion on Stalinvast had actually been intentional: the psychic force of the large number of deaths on Stalinvast served as the catalyst required to generate the Hydra, a bizarre Warp entity akin to a psychic virus.
This entity was created by the Ordo Hydra as part of a plan to ultimately destroy Chaos by transforming Mankind into a single hive mind using the Hydra and then deploying the united psychic force of the entire human race against the Dark Gods within the Immaterium. The only price would be the complete enslavement of Mankind and the loss of all individuality. The Hydra was first unleashed on Stalinvast as a latent mind-virus.
The Destruction of Stalinvast
Obispal was unknowingly being watched by the Ordo Malleus Inquisitor Jaq Draco and his retinue of Acolytes, who were tasked with making sure that Obispal successfully dealt with the rebellion -- though Draco may have been sent to Stalinvast for other more nefarious reasons, that he was not at the time aware of. Draco discovered the existence of the Hydra mind-virus, and being ignorant of the existence of the Ordo Hydra and of its misguided plans, thought the planet irredeemably lost to Chaos.
He subsequently ordered an Exterminatus on Stalinvast, but then rescinded the Order upon learning that the Hydra had withdrawn from the world. However, the Stalinvasti Astropath Moma Parsheen, who had been added to Draco's retinue after his arrival on Stalinvast, secretly sent the message on as vengeance for the suffering she had undergone at the hands of the Imperium because of her mutation. The Order was received by the Imperial Ravagers Space Marines who unleashed genocidal fury on Stalinvast.
Apparently unaware of the truth of the matter behind the Exterminatus Order, the Ordo Malleus later declared Draco Heretic and Renegade because of the unsanctioned and unnecessary genocidal action taken against an important Imperial world.
The Eldar and the Dead World
The Eldar later tried to use Stalinvast, by then a Dead World, as the site for an alien psychic ritual. This was due to the calamity which had befallen it and the residual energies that so much suffering left behind, which weakened the dimensional barriers between the Immaterium and realspace.
The ritual involved the presence of an Eldar "habitat" ship (a much smaller version of a Craftworld) and a performance by a Harlequin troupe. However the Eldar's plans were disrupted by the arrival of an Imperial Navy fleet, Inquisitors, and Space Marines, which apparently caused the Eldar to abandon their plans.
- The Inquisition War (Novel) by Ian Watson