“Joan!” Melinda called heedlessly as she supported me down the stairs. “Joan, we need help!”

Kindly-faced Joan appeared—as if by magic, though I was too cold and shaky to say for sure—in the doorway to one of the great ground-floor library rooms. She took one look at me, and her face seemed to go a few shades grayer.

“Can you do anything?” asked Melinda, more sharply than I expected. Joan bent and put a motherly hand to my forehead, as if feeling ...