The Horus Heresy was a cataclysmic civil war that occurred 10,000 years ago, pitting the Space Marines of the Imperium of Man against each other. The conflict began when the Warmaster Horus, once the most trusted servant of the Emperor, turned against his master and led a rebellion that would shatter the Imperium. The Horus Heresy would ultimately result in the destruction of the Imperium's unity, leaving it a shadow of its former self.
This is the critical caveat. Black Library (Games Workshop’s publishing arm) does not sell an official "Collection 109." They sell individual ebooks, bundles of 3, or the occasional Humble Bundle. horus heresy ebook collection 109
Let’s address the keyword directly. The "Horus Heresy ebook collection 109" refers to a digital compilation containing of the Horus Heresy series, plus the 55 separate novellas, short story anthologies, and "Primarchs" series entries that complete the timeline. The Horus Heresy was a cataclysmic civil war