The Grey Knights are all that stands between mankind and the ravages of Chaos. Since their secretive beginnings during the Horus Heresy, these legendary Space Marine daemon hunters have journeyed into the dark realms of the warp and beyond in pursuit of their supernatural enemies. Through an intensive regime of psychic training, new recruits are brought to the clandestine fortress of Titan to join the hallowed and vaunted ranks of the 666th Chapter. More than ever, these legendary battle-brothers must be vigilant and ever ready to defend the Imperium for the forces of Chaos are never truly defeated, and Armageddon beckons'

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It's a deep exploration of the Grey Knights and the events surrounding the First Armageddon War... including an appearance by the fearsome Angron, daemon primarch of the World Eaters.