From Restitution: Fire and fury:
“Cristóbal Navarro had been working at Sudeley Castle for weeks, posing as one of the stonemasons who were modifying a storeroom in the basement. He had observed Baron Seymour’s furtive movements and his paranoid security. All of which suggested a man with secrets.
And secrets intrigued Cristóbal.
Now, from his hiding place in an alcove where new masonry was being installed, Cristóbal watched as Thomas reached the end of the long corridor and pushed open a heavy wooden door. The hinges rotated silently. Thomas stepped through, and the door began to swing shut behind him.
Cristóbal moved, silent as a cat. Before the door closed, he slipped a thin piece of metal into the gap, just enough to leave a crack to peer through, but not enough for Thomas to notice from the inside.
The door settled against the shim with barely a whisper.
Cristóbal pressed his eye to the gap.
He knew the room beyond from earlier snooping. It was almost square, perhaps fifteen feet along each side, with a half-dozen old pews suitable for a private chapel or audience chamber, all piled toward the rear. It had stone walls, a flagstoned floor, and no windows. He had previously written it off as a storeroom.
He caught his breath as he watched Thomas approach one of the two iron cauldrons, each as tall as a man’s waist, positioned against the far wall like silent sentinels.
Thomas set down his lantern and a sack that clinked dully as though full of coins.
He lit a taper from the lantern and lowered it into the cauldron.
The flames that erupted seemed unnatural in the deconsecrated room, casting writhing shadows across the stone walls. Thomas repeated the process at the second cauldron. Now both cauldrons burned with the same eerie light, and the room pulsed with energy.”