A Lesson In Darkness is the third audio drama for The Horus Heresy - Primarchs series. A Lesson In Darkness was released as an MP3 format as part of the Black Library's 2017 Advent Calendar, on day 22.
Piamen is a tranquil world in the far reaches of the galaxy. Since throwing off the yoke of xenos invaders, they have remained free and peaceful...until the coming of the Imperium. When they refuse to join Mankind's star-spanning empire, a force of Legiones Astartes is despatched to bring the planet to Compliance. And when the Night Lords come, darkness falls. Piamen will never be the same...
- A Lesson In Darkness (Audio Drama) by Ian St. Martin