A sudden radiation storm forces the Sons of Horus ground troops underground and into a maze-like series of tunnels. There they encounter sheltered forces of the Dark Angels under Occultist Myrddin, and the two are forced into a brutal close quarters battle to secure passage beneath the rad wastes. The incomprehensible passageways split units from one another, and both Myrddin and Kagaddon are taken as casualties in the confusion. In the wake of their commander's injury, and the insane heroism of reaver Chieftain Malkos in the face of the powerful esoterist, the justaerin gain a foothold in one of the chambers, and the 1st legion retreat into the darkness of the tunnels.