Evening...
While Karl (and Ada?) was being shown around the town, and eventually his new workplace, and while Evelyn and June were buying supplies for future adventuring, other preparations were being made elsewhere in the city. By nightfall, those preparations were being put in motion...
It was past midnight when those who dwelled at the bottom the lake realized their sacred temple had been infiltrated, but by then it was already too late. When they arrived in the antechamber, which had been built to be dry and airtight, so as to preserve the idol from the erosion across the ages, they found not their idol, but an empty pedestal. And beyond that, a magical door formed on the far wall; a portal to another place much different from this undersea sanctuary, but one of which they knew well.
On the other side of the door stood a hooded man, smiling arrogantly as he gazed through the aperture at the furious dwellers. Perched in one of his hands sat the idol, in the other hand was held his wand, and behind him lie the city of the surface; Arcus Tuar. But they had only a glimpse, before a wave of the wand sealed the magical door, returning the stone wall to its natural state.
There was only one way now to recover their most revered treasure. If the man sought asylum with the surface folk above, then the dwellers would summon their legions and rise to the surface for the first time in generations. Once there, they would tear the city and its people apart, brick by brick and bone by bone if they had to, until this thief was found, and that which he had stolen was returned to its rightful place in the depths...