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.

For Ianthe, war is all too familiar. A former soldier in the Astra Militarum, she now serves Inquisitor Covenant as an agent of the Throne. Her first mission sees her investigating a cult called the Children of Eternity. Falling foul of the local Enforcers, Ianthe soon learns that war in the shadows is seldom straightforward and that the local, angry law-keepers are the least of her troubles.

After seven years of bitter war, the end has come at last for the conflict known infamously as the Horus Heresy. Terra now lies within the Warmaster’s sights, the Throneworld and the seat of his father’s rule. Horus’ desire is nothing less than the death of the Emperor of Mankind and the utter subjugation of the Imperium. He has become the ascendant vessel of Chaos and amassed a terrible army with which to enact his will and vengeance. But the way to the Throne will be hard as the primarch Rogal Dorn, the Praetorian and protector of Terra, marshals the defences.

Valorous Heart. Our Martyred Lady. Bloody Rose. These names of Adepta Sororitas orders are famed across the galaxy, as are the Battle Sisters who serve the emperor's will. To die in the name of the God-Emperor of Mankind is to live eternal, and none are more willing to bleed in his name than the Adepta Sororitas - the Sisters of Battle. The Book of Martyrs charts the deaths of these exemplars.

Opal is a gleaming shrine world of saints and soldiers, beloved of the Emperor Himself. Sent to retrieve the skull of the revered Saint Veres, Sister Superior Augusta of the Order of the Bloody Rose and her squad find themselves in the midst of the capital’s holiest festival, a time of reverence and celebration. But all is not well – despite what its planetary leaders would have Augusta believe, political danger bubbles under the surface, and rebel attacks gnaw away at the city’s outskirts. The greatest threat, however, is yet to come.