Mara couldn't have known whether the boy in the photograph was Lucas. Names are loose ends; they belong to many hands. But the stair had been connected where the steps used to be, and in that connection something practical became kind.

: Details on how the treads are mounted—whether they are "raised" on top of the stringers or "concealed" between them for a sleeker profile. Structural Connections

: For a comfortable rhythm, the sum of one riser and one tread should approximately equal 27 inches (e.g., 7" riser + 20" tread).

Use heavy lines for the structural stringers and lighter lines for hatching and dimensions to ensure the print is readable.

"You architects keep finding our ghosts," he said. He led Mara down a service corridor into a shaft of dust and green paint flakes. The stair — the double stringer — sat exposed in the atrium like a ribcage. No treads. The stringers arched two parallel bones from mezzanine to landing, bolts like teeth.