"Death is all around us now: the death of the body, the death of the spirit, but most of all the death of hope."


The Horus Heresy: Book One - Betrayal is the first book released as part of Forge World's Horus Heresy Series of campaign and army books that takes place during the Horus Heresy. The book deals with the events starting near the end of the Great Crusade and includes the Istvaan III Atrocity. It contains rules and special characters for the pre-Heresy Sons of Horus, World Eaters, Emperor's Children, and Death Guard Legions as well as a Space Marine Crusade Legion army list.

Official Synopsis

The Horus Heresy: Book One - Betrayal is a supplement for Warhammer 40,000 dealing with war and battle in the dark age of the Horus Heresy. This book, lavishly illustrated in full colour, contains extensive background information on the Imperium as it stood at the end of the Great Crusade. Also detailed are the histories of the four Space Marine Legions who took part in the Istvaan III Atrocity: the Sons of Horus, Emperor's Children, World Eaters and Death Guard and an extensive campaign system.

This book also contains a complete Space Marine Legion Crusade army list as well as games rules for the Primarchs of the four Legions, super-heavy vehicles and special characters featured in the story.

This is a bonded leather-bound, full-colour 289-page hardback book.


The following is every section contained within The Horus Heresy Book One - Betrayal:

  • Preface - The preface of this book, and all other Forge World Horus Heresy books to follow begin with a foreword by the in-universe "author" of the book, an unknown individual who signs with the letters AK.
  • Imperialis Dominatus - A Great Crusade-era map that covers two full pages, and includes the names of many notable planets and locations.
  • Age of the Emperor - A short retelling of the history of the Imperium of Man up to the end of the Great Crusade. This includes the Age of Strife, the Unification Wars, the Treaty of Mars, the later Great Crusade and Horus' fall. Also included is information regarding the Primarchs, the Warp and Navigators, the Astra Telepathica and Psykers, the Astronomican, basic Space Marine armour and weapons, and the High Lords of Terra.
  • The Legiones Astartes - This section contains information regarding the twenty Space Marine Legions including their origins, Space Marine initiation and organ implantation processes, and their role within the Imperium.
  • Crusade Legion Disposition - A two page layout of a basic Space Marine Legion command structure and strategic disposition along with other additional information.
  • The Death of Isstvan III - This section describes the Isstvan System, its initial Imperial Compliance and rebellion, the Battle of Isstvan III and the Istvaan III Atrocity from the Loyalists' planetfall to the Traitor Legions' Virus Bombardment of Istvaan III's surface.
    • Part 1: Treachery
    • Part 2: Ruin
    • Part 3: Extermination
  • The Death of Isstvan III Campaign - This section describes a six-mission campaign for reenacting the Istvaan III Atrocity on the tabletop and three "legendary battles" and terrain information.
    • The Death of Isstvan III Campaign
    • Campaign Phases
    • Isstvan III Battle Missions
    • Deployment Maps
    • Mission 1: Blood Fued
    • Mission 2: Fire Tide
    • Mission 3: Shatter Strike
    • Mission 4: Onslaught
    • Mission 5: Dominion
    • Mission 6: Extermination
    • 'Cometh the Red Angel'
    • 'The Flight of Truth'
    • 'The Death of Gods and Angels'
    • Isstvan III Battlefield Terrain
  • Campaign Appendix: Zone Mortalis - This section contains the rules necessary for a Zone Mortalis battleground, which is fighting in confined spaces such as starships, underground areas, and narrow urban environments.
    • Campaign Appendix: Zone Mortalis
    • Zone Mortalis Assault Mission
    • Zone Mortalis Encounter Mission
    • Isstvan III Zone Mortalis Stratagems
  • Age of Darkness Battles - This section contains the rules necessary for a Space Marine Legion army list that is set in the late Great Crusade and early Horus Heresy eras. It includes force organisation charts, an allies matrix, units, armour, and wargear available to the Legiones Astartes in general.
    • Age of Darkness Battles
    • Age of Darkness Allies Chart
  • Space Marine Crusade Legion Army List - This section contains the rules for the various units used by the Space Marines Legions during the Istvaan III Atrocity.
    • Space Marine Legion Warlord Traits
    • Headquarters
    • Elites
    • Troops
    • Dedicated Transports
    • Fast Attack
    • Heavy Support
    • Lords of War
    • Space Marine Legion Wargear
  • Space Marine Crusade Legion Appendix - This section contains the rules, Legion-specific units, and special characters for the four Legions the took part in the Istvaan III Atrocity.
    • The Sons of Horus
    • The World Eaters
    • The Emperor's Children
    • The Death Guard
  • Mechanicum Army List Appendix - This section contains the rules and units nessecary for building an Mechanicum allied force for a Legiones Astartes army.
    • Mechanicum Army List Appendix
    • Lords of War
    • Calleb Decima
  • Apocalypse Rules Appendix - This sections contains a condensed reference of the rules nessecary for a Warhammer 40,000 Apocalypse game.
    • Appendix I: Super-Heavy Vehicles
    • Appendix II: Gargantuan Creatures
    • Appendix III: Super-Heavy Flyers
    • Appendix IV: Additional Special Rules
  • New Special Rules Summery - This section summarises various special rules found within the book, and also includes the four different versions of the 'Legiones Astartes' rule used by the four Legion features in the book.
  • Afterword - An afterword about the Horus Heresy and Warhammer 40,000 by the book's real-world author, Alan Bligh.

Included Legion Specific Army Rules

The following is a list of included unit rules that are specific to a certain Legion only:

Included Non-Legion Specific Army Rules

The following is a list of included unit rules that are able to be taken by all Space Marine Legions:

Included Mechanicum Army Rules

The following is a list of included unit rules that are able to be taken by a Mechanicum Army:


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