In the Pandorax System, on the death world of Pythos, an ancient secret that has laid buried for millennia has been unearthed.... Ignorant of this terror, troopers of the Catachan 183rd, stranded on Pythos and under the command of Colonel 'Death' Strike, find themselves under attack by the forces of Chaos. Daemons in their thousands flock the sky, and none other than Warmaster Abaddon leads the attack. With the Death Guard and Black Legion arrayed against them, the Catachans appear to be doomed, until salvation arrives in the form of the entire Dark Angels Chapter, led by Master Azrael and a host of heroes. But what is the so-called 'Damnation Cache'? What secrets does it harbour and why has it also attracted the attention of the daemon-hunting Grey Knights?