She smiled. Somewhere, Arjun Nair was laughing. His echo had been found.

She opened the section of the documentation for the hundredth time. And there it was: “Eigenvalue extraction is not about finding the strongest mode. It is about listening to the quietest one.”

Mira spent three months in the SAP2000 documentation. She learned about from a case study of the Leaning Tower of Pisa. She mastered cable elements from a buried tutorial on the Millau Viaduct. She discovered that her grandfather had used a hidden API script —documented only in a changelog from 2018—to simulate the river’s seasonal flow against the piers.

Then she remembered the “echo.”

She ran a modal analysis. The first five modes were ugly—torsion, sway, vertical bounce. But the sixth mode? A gentle, almost imperceptible lateral sway with a period of 4.7 seconds. That was the bridge’s “echo.” That was the frequency at which the old steel wanted to move.