The Great Angel, Sanguinius, lies slain at his brother's hand. Terra burns as reality itself unravels and the greatest bastion of civilisation teeters on the brink of annihilation. Desperate defenders gather, banding against the rabid traitor hordes. The Hollow Mountain, host to the pilgrims of Euphrati Keeler, is one of the last redoubts, held by the Dark Angels while the unclean host of Typhus lays siege. Malcador the Sigillite sits ablaze on the Golden Throne, trying to buy his master more time. But time is running out... Guilliman races across the stars to reinforce the Throneworld. Will he return to ashes, where a Warmaster of Chaos has ascended to godhood, or will the Emperor have triumphed? And at what cost? It all comes down to one final, climactic confrontation: the Emperor versus Horus. The father against the son.