Ciaphas Cain - Ghosts of Perlia: Cain's actions on the world of Perlia would come back to haunt him on two occasions during the eighty standard years between the first and second sieges of that planet.The first occurred during the campaign on Periremunda, when Cain discovered that the Ordo Xenos and the Adeptus Mechanicus had been working on a secret project surrounding an artefact known as the Shadowlight.This unusual artefact, which predated the existence of Mankind itself, activated the powers of latent psykers and boosted the powers of already active ones. The Shadowlight had been contained in a secret Mechanicus shrine located within the hydroelectric dam in the Valley of Daemons on Perlia's eastern continent, until it was stolen by a rogue tech-priest named Metheius, in the employ of Inquisitor Killian of the Ordo Hereticus.When Cain arrived at the dam -- shortly before destroying it, flooding the valley and drowning thousands of Orks -- he found that the Tech-priests of the shrine had been killed with surgical precision only solar weeks before. He learned standard years later that this had been the work of Killian and Metheius, Killian having co-opted the services of an Adepta Sororitas force to raid the shrine.Killian had allied with a number of Chaos Cults on Periremunda and intended to use the Shadowlight to boost their psychic powers, turning them into servants of the Emperor without them realizing it. His ultimate plan was to use the Shadowlight to create an army of psykers powerful enough to storm the Eye of Terror and take the fight to the forces of Chaos on their own ground (a plan that another psyker deemed could potentially have caused the destruction of the galaxy).At Inquisitor Amberley Vail's behest, Cain assisted in tracking Killian down to his lair at an Adepta Sororitas convent on Periremunda. Having already made several attempts to assassinate Cain, Killian tried to win the commissar over as an ally, but upon learning of Killian's deranged plans and discovering he was using a captive Lictor to lure in a nearby Tyranid swarm to cover his tracks, uncaring of the civilian casualties his escape plan would incur, Cain refused him and a firefight broke out.In the confusion, Jurgen grabbed the Shadowlight and Killian, unaware Jurgen was a Psychic Blank, made the mistake of assuming Cain or the Mechanicus had found a way to deactivate the device. He seized the Shadowlight from Jurgen and attempted to make a break for it, only to be fatally exposed to its full power once he was out of range of Jurgen's abilities. Methius, who was accompanying Killian, was later killed by Tyranid Gargoyles during the evacuation of the convent before Vail called in an orbital bombardment to exterminate the Tyranids.After Killian's death, the Shadowlight was returned to Perlia in the shrine set in the rebuilt dam in the Valley of Daemons, where it would remain for another sixty standard years.The other occasion when Cain's actions on Perlia would come back to haunt him was during the Second Siege of Perlia, in 999.M41. Cain had by that time retired and made Perlia his home, teaching at a Schola Progenium on the western continent, in a mountainous village near the planetary capital of Havensdown.Meeting with the Rogue Trader Orelius, whom he had met on Gravalax, Cain discovered that there was a Chaos force headed in the direction of Perlia, having overrun two neighboring star systems. It was Cain's suspicion (and Inquisitor Vail's as well, as she had sent Orelius to meet with Cain) that the Chaos horde and their leader, Warmaster Varan the Undefeatable, had their sights set on the acquisition of the Shadowlight artefact, potentially either at the behest of Abaddon the Despoiler or to gain his favour.Called once again to defend Perlia, Cain coordinated with the commanders of the Planetary and System Defense Forces, appearing in pictcasts calling for civilians to join the militia, and leading attacks against Chaos insurgents, culminating in a final showdown with Warmaster Varan himself. Though Cain succeeded in killing Varan and effectively ending the Second Siege of Perlia, the Shadowlight was taken by a Necron scouting party, presumably to destroy it as psykers were the most potent weapons that could be used against the Necrons.From the Necrons' actions Cain and Amberley Vail theorised that the Shadowlight may have been built by the Old Ones in order to combat the Necrons, who had a documented fear of the Warp and psychic powers. While not an ideal resolution, Cain and Vail concluded that if the Necrons had feared the Shadowlight so, they likely had no plans to use it against the Imperium, which made it preferable for the artefact to be in their hands, rather than those of the forces of Chaos.