The Sons decided to rest and recuperate at the church.
While sleeping, Nevron and Urnyx were transported(?) back in time to the same day long ago, when the underground city below Ironville was still alive and populated. There they participated in a giant ritual that captured Garos the Eternal Champion, First Lieutenant of the Arch-angel Saint Michael (Leader of the Armies of Heaven) so that the city, lead by high priest Kyrosh of the Twins could strike a deal with none other than Ter-Zoth, the demon that the Sons had liberated some months earlier, to have the demons leave the city alone.
Even though the two Sons sabotaged the ritual, so that the crystal would no longer be unbreakable, it still formed and trapped the angel. Ter-Zoth arrived, but didn't uphold his end of the bargain and instead flooded the underground city with bone demons. The Sons desperately tried to hold back the tide of fiends, but to no avail and were soon ripped to pieces, while Ter-Zoth teleported away with the coffin, after failing to bring it back to Hell through the gate he had opened.
Weird thing was, that while Nevron and Urnyx were still themselves, both were followers of the Twins and everybody called them by their real name and seemed to know them. Apparently, they had even gotten the crystal that was grown around Garos for the high priest by going up to the surface and into Oakwood, which was, according to the people of the underground city, no mean feat.