“Well done,” says Edwin. “The cup to Asia.”

She lets go of Edwin’s arm and drops a curtsey that sends the hoop of her skirt swinging like a bell. She takes Jean’s soft hand in her own. “ ‘There was a star danced, and under that were you born,’ ” she tells Jean. She looks from John to Edwin. Both have ceased to pay attention. Both are staring out over the water toward the dark shore. “Don’t you think so?” she asks them insistently. “Isn’t that our Jean to a turn?”

vi

Edwin has booked them into rooms in Cataract House, an enormous, elegant five-story hotel, which, had they only known it, is one of the last stops on the Underground Railroad. There is no sign of this.

They breakfast in a dining hall with high ceilings and tall windows. Asia’s chair gives her a view of the green-and-white rapids rushing past. While they wait for their food, John tells a story about an addlepated actor in the Philadelphia company.

“The play was Lucretia Borgia,” John says, “and the scene the one in which the four soldiers find her on the street to enact their revenge. So the line is supposed to be ‘I am Ascanio Petrucci, madame, cousin of Pandolfo Petrucci, Lord of Sienna, who was assassinated by your order . . .’ But this foozler can’t come up with it to save his life. He bumbles and stumbles about and finally he just up and says, ‘Damn it all, who am I again?’ There’s old Lucretia on her knees, begging for her life, and everything has to stop, the audience is laughing so hard.”

Of course, the addlepate in John’s story is John himself. Asia wonders if he really thinks they don’t all know this. It was a blunder heard round the world, this son of Junius Booth who turned the tragedy of Lucretia Borgia into farce. The actress playing Lucretia will never forgive him for destroying her big scene.

Their guide comes to fetch them, an Irishman named Patrick Burke. Mr. Burke looks to be in his early fifties, with hardened skin like a sailor. He takes them to the top of the American Falls, then down Biddle’s staircase to the base. Great clouds are gathered above the water. Asia counts nine rainbows, some bright and in complete rings, some faint and fragmented. Her face is dewy with mist.

Mr. Burke tells them, shouting to be heard, that a few years back an enormous boulder detached from the cliffs and fell into the gorge, narrowly missing the staircase while he himself was inside. A few feet closer and neither he nor the staircase would be standing today. “I felt the careless finger of God,” Mr. Burke says, “just scratching an itch.”