Iseult holds a piece of blue to the loft window. The color lands on your wrist like a cool coin.

“Bigger glass wants a wall that is not all wall,” she says. “Flyers take shove. Pointed ribs send more load down. Then a mason can open a hole that would have frightened a nave-builder. The hole is my country. Geometry is the border treaty.”

She shows you a cartoon—the drawn plan of a window—pricked for transfer. It is a tracing floor in miniature, vertical, destined to glow.

Gareth, in the yard below, is not evil for loving thick stone. He learned a different treaty. The choir is a new one.

Canon Odo’s voice floats from the cloister, arguing mildly with Peverel about Saint Brice’s day and whether God minds a leak.

You mind a leak. Iseult minds a leak. The glass will mind.

The old nave’s windows are slits because thick walls are busy being buttresses in themselves. The choir wants a wall like a ribcage, flyers for elbows, glass for lungs. You understand it better when color sits on your wrist. Odo will understand it better if someone says shove instead of beauty.