The Damnation of Pythos

"Thinning the veil"

- Book's tag-line

The Damnation of Pythos is the thirtieth volume of the Horus Heresy series of novels.

Synopsis
In the aftermath of the Dropsite Massacre at Istvaan V, a battered and bloodied force of Iron Hands, Raven Guard and Salamanders regroups on a seemingly insignificant death world. Fending off attacks from all manner of monstrous creatures, the fractious allies find hope in the form of human refugees fleeing from the growing war, and cast adrift upon the tides of the warp. But even as the Space Marines carve out a sanctuary for them in the jungles of Pythos, a darkness gathers that threatens to consume them all…

Trivia
The Damnation of Pythos is a far prequel to the Warhammer 40,000 Space Marine Battles Series title Pandorax, which takes place on Pythos nearly 10,000 years later.

Source

 * The Damnation of Pythos by David Annandale