Liar's Due (The Horus Heresy)

News has reached Town Forty-Four, on the tranquil world of Virger-Mos Terra has fallen, the Emperor is dead and the Imperium belongs to Horus Lupercal. As the people of Forty-Four struggle to deal with this revelation and the rest of the planet falls into anarchy, Leon Kyyter begins to doubt the news, along with the stranger from Terra, the remembrancer with the odd tattoo...

Read it because
It shows how the worlds of the Imperium react to news of the Warmaster's treachery, and to what lengths Horus' followers will go to ensure support and victory...