2nd Black Crusade

In 597.M32, the Warmaster of Chaos, Abaddon the Despoiler launched his second offensive against the Imperium of Man and initiated the Second Black Crusade. This time, Abaddon places a terrible curse upon the worlds of the Belis Corona Sector, infusing them with the touch of the Warp. Meanwhile, his Black Fleet attacks the sector's Imperial shipyards, destroying dozens of Imperial Cruisers being constructed or repaired. Before the Imperium can muster its strength to fight back, the Despoiler retreats into the Eye of Terror, his works complete.

History
As part of the Second Black Crusade Abaddon wove a terrible hex upon a number of worlds close to the Eye of Terror, seeding them with the taint of the Dark Gods. Leading a small band of his elite warriors, Abaddon breached the Imperial Navy base in Belis Corona. While his fleet launched a diversionary attack against the shipyards, Abaddon and his Bringers of Despair (the Warmaster's strongest and most vicious of his Terminator elite) landed on one of the system's outermost moons. Slaughtering the garrison, the Warmaster crafted a complex ritual using their mangled remains and invoking a curse that would sink deep into the core of the moon. Only centuries later would the curse awaken at the Despoiler's behest and do its terrible work, unleashing a mutagenic plague upon the defenders stationed there. By the time Battlefleet Corona had mustered to repel the attacks on the core worlds of Belis Corona, Abaddon had already departed, his mission complete.

Shortly after the assault on the shipyards of Belis Corona, an attack occurred on the Inquisitorial vaults of Nemesis Tessera. Hidden beneath layers of ice and snow, the Holy Ordos had constructed a watch station from which to study the Eye of Terror along with hexagramatically warded cells to hold daemonic prisoners. It remains unknown as the whether this was the work of Abaddon, but in a swift and brutal assault, one of the cells deep beneath the station was opened and its daemonic inhabitant released. By the time Inquisitorial forces had secured the facility, the attackers were gone, leaving only a trail of smoking corpses and spent bolt shells to mark their passage.