The Citicorp tower in New York stands on four giant stilts placed at the middle of each side, not at the corners, because a church owned the corner of the block and the bank built over it. In June 1978, a year after it opened, a Princeton engineering student named Diane Hartley, writing a thesis about the building, phoned the structural engineer’s office to ask about winds hitting it diagonally, at the corners. Around the same time the engineer, William LeMessurier, went back over those diagonal winds himself, and found that the welded joints he had specified had been swapped for cheaper bolted ones, and that a strong enough storm could pull them apart. All that summer welders came in at night to plate the joints over, and the offices opened every morning as usual. In September a hurricane came up the coast and turned out to sea. The story stayed private for seventeen years. The question that started it wasn’t clever. It was the plain one, the kind a student is supposed to ask, about the wind from the direction nobody had drawn.