Warhammer 40k - Dark Angels Novel - Angels of Darkness by Gav Thorpe

The Dark Angels Space Marines are amongst the most devout of the God-Emperor's servants. Their loyalty is seemingly beyond question and their faith almost fanatical. Yet the Chapter harbours a dark and horrific secret that stretches back over ten thousand years to the time of the Horus Heresy. When Dark Angels Chaplain Boreas captures and interrogates one of the Fallen, the past collides with the future with tragic consequences.