Under the benevolent leadership of the Immortal Emperor the Imperium of Man has stretched out across the galaxy. On the eve of victory, the Emperor leaves the front lines, entrusting the great crusade to his favorite son, Horus. Promoted to Warmaster, the idealistic Horus tries to carry out the Emperor'sgrand design, all the while the seeds of heresy and rebellion have been sowed amongst his brothers.

Far from Terra, the XVIth Legion continue in the Great Crusade as the 'Sons of Horus'. Putting the debacle with the interex behind him, the Warmaster has become more withdrawnas he struggles to deal with the jealousy of his brother primarchs, and increasingly relies on the council of his advisors as he plans each new campaign. Noble captain Garviel Loken harbours misgivings about the clandestine ways adopted by many of his brethren, but when the Legion is sent to reconquer the moon of Davin, it is clear that Horus has a personal stake in the matter which may have clouded his judgement. With dark forces rising against them, have the pimarch and his warriors been drawn into a trap?

Having made a miraculous recovery from the grevious injuries he suffered on Davin, Warmaster Horus now leads the triumphant Imperial forces against the rebel world of Isstvan III. An unprecedented alliance between the Sons of Horus, Death Guard, World Eaters and Emperor' Children Legions seems more than capable of overwhelming the paltry mortal defences - indeed, such a display of force seems unneccesary? Putting their own concerns aside, Garviel Loken and his loyal kinsmen lead their companies to the surface only to learn the full, horrifying truth, and the legendary war known as the Horus Heresy begins with the most foul act of betrayal imaginable...

Having witnessed the terrible massacre of Imperial forces on Isstvan III, Death Guard Captain Garro seizes a ship and sets a course for Terra to warn the Emperor of Horus's treachery. But when the fleeing Eisenstein is damaged by enemy fire, it becomes stranded in the warp - the realm of the Dark Powers. Can Garro and his men survive the depredations of Chaos and get his warning to the Emperor before Horus's plans reach fruition?

Under the command of the newly appointed Warmaster Horus, the Great Crusade continues. Fulgrim, Primarch of the Emperor's Children, leads his warriors into battle against a vile alien foe, unaware of the darker forces that have already set their sights upon the Imperium of Man.

The planet of Caliban exists much as it has for thousands of years - the knightly orders protect the common people, fighting back the beasts that lurk in the depths of the seemingly endless forests. Young Zahariel and Nemiel aspire to join the greatest of the orders, led by the example of mighty Lion El'Jonson and his vision of a peaceful and unified world. But the coming of the Imperium brings new concerns and a new destiny for the Lion as part of the Great Crusade, and the sons of Caliban must decide if they will follow him to glory among the stars.