The planet housed an Imperial research facility where members of the Adeptus Mechanicus worked on projects for the Imperial Navy, such as new propulsion drives and laser technologies. Their research involved classified artefacts and relics; there was a risk of researching heretical subjects. Then, without warning, Geonide faced open rebellion in its cities, taking a heavy toll on the population and the research facilities.
It was discovered that a group of latent psykers were tainted by the lies of Chaos. They opened a rift in reality by using the energies of the Warp. Within a year, 75% of Geonide's population had fallen to Chaos and formed an army, supplemented by daemons and other warp-spawned creatures.
Normal methods for reclaiming the planet failed and the Inquisition called for an Exterminatus. However, before the world was annihilated, the Black Templars were dispatched to retrieve valuable artefacts, research documents and Imperial personnel that were not tainted by Chaos.