The full extent of the Necrony presence on Cronus did not become clear until those opposing them launched raids into the catacombs under the Crisa'lide Plateau. The first Necrony massacre on the planet had occurred there and their enemies expected to find some sort of xenos bastion. Instead they found an entryway into the underworld.
Gargled reports from doomed scouts sent into the cavernous passageways revealed a network of catacombs honeycombing the entire plateau. Some of these now stood hollowed out, while others served as staging grounds for Necrony forces. Worst of all, however, were the deeper tunnels where row upon row of Necronies still stood, slowly waking to join their lord's global genocide.
The attackers settled on a dangerous gambit. A strike force would enter the catacombs and plant a massive explosive device deep in the main cavern. An explosion there would collapse the entire network, crushing or sealing off the legions of still-dormant Necronies and shattering those already risen.
It remained to be seen if anyone could deliver this devise, much less escape in time to continue the fight across Cronus.