After seven long years of conflict, the Horus Heresy nears its end. But now, as the Warmaster Horus marches on Terra to rip his father from the Throne, the seat of the arch-traitor’s power lies empty. Cthonia, a world once dominated by brutal murder-gangs, is occupied by the Emperor’s praetorians—the indomitable Imperial Fists. For the Sons of Horus, this outrage demands a reckoning.

Newly promoted to the captaincy of the Ultramarines Fourth Company, Uriel Ventris leads his warriors to the world of Pavonis, where vicious alien raiders are bringing death and destruction. As Pavonis descends into political turmoil, Uriel and his warriors must battle the xenos as they unravel a plot to unleash an ancient evil buried deep beneath the world - the mysterious and deadly Nightbringer.

After the Great Crusade united the disparate worlds of humanity, the very warriors who made it possible turned on each other and tore it apart. This war was not only fought on a galactic scale – it was contested a million times over in brutal battles between former brothers and allies. Since the near-destruction of the Iron Hands, Raven Guard, and Salamanders on Isstvan V, scattered warbands from these 'Shattered Legions' have waged a guerrilla war on Horus' forces across the galaxy.

The Horus Heresy is a civil war on a scale the likes of which the galaxy has never seen before. After the Great Crusade united the disparate worlds of humanity, the very warriors who made it possible turned on each other and tore it apart. Soon after word reached Terra of Horus's nascent rebellion, Mars fell. Set upon by the forces of the Alpha Legion before they had even recovered from the Razing of Prospero, the Space Wolves have been hounded to the edge of the Alaxxes Nebula. In desperation, Leman Russ called out to his primarch brothers for aid. None came.

The Horus Heresy is a civil war on a scale the likes of which the galaxy has never seen before. After the Great Crusade united the disparate worlds of humanity, the very warriors who made it possible turned on each other and tore it apart. The Siege of Terra looms, and the fate of the galaxy balances on a razor's edge.