Corvin’s hands were shaking so wildly that the tea in his tin mug slopped over the rim, sizzling on the hot stones of the charcoal fire bowl. Sister Merrow took the mug from him, pressed a thick slice of sourdough crust into his fingers. Then she wrapped a warm woolen shawl around his trembling shoulders. The scent of boiled chicory and woodsmoke gradually brought the color back into the young man’s cheeks.
‘I went down to Sub-Vault Seven at midnight,’ Corvin whispered, glancing nervously toward the half-open window as if he expected academy court guards to leap through the glass. ‘Master Sorell ordered all junior apprentices confined to their bunkhouse quarters. But I have the upkeep keys for the drainage galleries from my work with Candidate Rook on the stone-carrier experiment.’
He reached into the lining of his cloak. Then he pulled out a rolled sheet of heavy master builder’s linen, stained with grease pencils and black sewer grime. He unrolled it on the frame stand table. He showed a careful, hand-drawn height of the foundations beneath the High Sluice.
‘Look here,’ Corvin said. His finger shook as he pointed to a massive vaulted chamber labeled Sub-Basement Cistern 4. ‘This chamber was built during the great flood of sixty-two. It’s an emergency surge tank carved directly out of the solid mountain stone, eighty feet long, forty feet wide, and thirty feet deep. It holds over eighty thousand gallons of water.’
