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 Legions who took part: 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.