"War is the crucible in which we burn."
The Horus Heresy: Book Two - Massacre is the second 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 of the Drop Site Massacre of Istvaan V. The book contains rules and special characters for the pre-Heresy Iron Hands, Salamanders, Night Lords, and Word Bearers Legions as well as an updated Space Marine Crusade Legion army list.
Word of the Warmaster Horus' treachery escapes Isstvan III and now the Space Marine Legions loyal to the Emperor mobilise to make Horus and those who follow him account for their crimes. However the depth of the betrayal is yet to be revealed.
The Horus Heresy Book Two - Massacre is lavishly illustrated in full colour and contains the dark deeds leading up to the terrible slaughter that unfolded during the Drop Site Massacre on Isstvan V. Also detailed are the histories of four of the Legions that took part: The Iron Hands, Salamanders, Night Lords and Word Bearers, and an extensive campaign system so you can play out the battles on the tabletop. This book also contains additional entries for the Space Marine Legion Crusade Army list presented in The Horus Heresy: Book One - Betrayal, as well as games rules for the Primarchs of the four newly described Legions, super-heavy vehicles and special characters featured in the story.
The following is every section contained within The Horus Heresy Book Two - Massacre:
- Preface - The preface of this book, and all other Forge World Horus Heresy books begin with a foreword by the in-universe "author" of the book, an unknown individual who signs with the initials AK.
- Imperialis Dominatus - A Great Crusade-era map that covers two full pages, and includes the names of many notable worlds and locations. This is the same map included in The Horus Heresy: Book One – Betrayal.
- The Road to War - 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 beginning of the Great Crusade, Horus' becoming Warmaster and his eventual fall to Chaos, and the Istvaan III Atrocity. Also included is information regarding the heavy support wargear of the Legiones Astartes, a short list of notable campaigns and events that occured near the end of the Great Crusade and the Space Marine Legions that took part in them.
- The Dropsite Massacre - This section contains a summary of the Drop Site Massacre, from the initial scans of the Isstvan System by Loyalist forces and their initial planetfall, to the landing of the second wave of supposedly Loyalist forces, and then on to the Drop Site Massacre itself. Also included are detailed maps of the Isstvan System and the Urgall Depression where the battle unfolded, an interrogation report transcript from a captured Word Bearers Astartes, and a highly detailed look at the Thallax warriors of the Mechanicum. This section begins at Planetfall: Minus 339 Hours Terran Sidereal and ends at Planetfall: Plus 3.9 Hours, with over two hundred thousand Astates and one Primarch dead.
- Part 1: Invasion
- Part 2: The First Wave
- Part 3: Massacre
- The Space Marine Legions - This section contains updated information on the Sons of Horus, World Eaters, Emperor's Children, and Death Guard Legions. This section also includes an in-depth look at the history, disposition, and notable battles of the Iron Hands, Night Lords, Salamanders, and Word Bearers Legions, along with Legio Atarus Titan Legion.
- Battles in the Age of Darkness - This section contains expanded rules for Warhammer 40,000 intended for games between regular and Apocalypse scale battles during the Great Crusade and Horus Heresy.
- The Lords of War
- Battles in the Age of Darkness Force Organisation Charts
- Battles in the Age of Darkness Additional Special Rules
- Force Organisation Chart Referrence
- The Dropsite Massacre Campaign - This section describes how to reenact the Dropsite Massacre on the tabletop or exploring possible alternate outcomes of pivotal moments.
- How the Dropsite Massacre Campaign Works
- Optional Campaign Rules
- Phase I - The Loyalists Strike
- Phase II - The Imperium Bleeds
- Phase III - Blood and Treachery
- Mission I - Brother against Brother
- Mission II - Hammerblow Assault
- Mission III - Deadly Ground
- Mission IV - Tide of War
- Legendary Mission: Vanguard Fury
- Legendary Mission: Cataclysm
- Legendary Mission: The Blood of the Primarch
- Space Marine Legion Crusade Army List Additions and Updates - This section includes rules that expands upon the Space Marine Legion Crusade Army List found in The Horus Heresy: Book One - Betrayal.
- Additional Special Rules for Heresy-era Gaming
- Fast Attack
- Heavy Support
- Dedicated Transports
- Lords of War
- Space Marine Legion Army List Appendix - This section contains the rules, options, and special characters for the eight of the eleven Space Marine Legions that were on Isstvan V.
- The Legio Cybernetica - This section contains the rules and units needed for building Mechanicum force, either as a standalone army or as an allied detachment to a Legiones Astartes force.
- Mechanicum Warlord Traits
- Legio Cybernetica Wargear and Special Rules
- Fast Attack
- Heavy Support
- Appendix: Battles in the Age of Darkness - This section contains rules for using super-heavy units and apocalyptic weapons in Age of Darkness battles.
- Super-Heavy Vehicles and Gargantuan Creatures
- Super-Heavy Walkers
- Apocalyptic Weapons Rules
- 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:
- The Sons of Horus
- The World Eaters
- The Emperor's Children
- The Death Guard
- The Iron Hands
- The Night Lords
- The Salamanders
- The Word Bearers
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:
- Legion Mortis Dreadnought
- Legion Contemptor-Mortis Dreadnought
- Legion Tarantula Sentry Gun Battery
- Primaris-Lightning Strike Fighter
- Legion Javelin Attack Speeder Squadron
- Legion Deathstorm Drop Pod
- Legion Deimos Whirlwind Scorpius
- Legion Sicaran Battle Tank
- Legion Dreadnought Drop Pod
- Legion Glaive Super-Heavy Spacial Weapons Tank
Included Mechanicum Army Rules
The following is a list of included unit rules that are able to be taken by a Mechanicum Army:
- Magos Dominus
- Enginseer Auxillia
- Myrmidon Secutors
- Mechanicum Thallax Cohort
- Legio Cybernetica Castellax-class Battle Automata
- Tech-Thrall Adsecularis
- Crusade Fleet Support Wing
- Myrmidon Destructors