They came to the last two panels. Boyd said: "Finally we returned to our home and rebuilt it as a place safe from the Xeelee." The first panel showed a sphere, blue capped with fat brown poles. Painted onto the central cerulean band were clouds and a tiny Sun that twinkled along the equator. The fringes of the polar caps held a lot of detail: sideways-on pictures of trees and men, oriented as if the clouds were "up" and the poles were "down." "I don't understand this one," Boyd admitted. "Maybe it was a stage in the Shell's construction. But here's the world as it is now." The last image was crudely sketched on the surface of the wall, with no depth or animation. It showed a globe with a Shell around it. Allel picked at flaking paint. Boyd coughed self-consciously. "So, you understand now why I brought you here?"

Allel inspected paint dust. "This is just dyed cow-tree milk. This last picture must have been added much later--"

Boyd swore. She spat on the smooth floor and stalked out.

...And, thought Allel, excited, in that case maybe the world was more like the other image, the blue sphere. But what did it mean? Everyone knew there was a Shell around the world -- you could see it...

She became aware of her mother's absence. Cursing, she hurried out.

Boyd stood a few paces from the door, fists clenched. Feathers of snow drifted around her legs. "I repeat. Why do you think I brought you here?"

Allel tried to concentrate on the question. "To show me this place? To tell me its story?"

"Yes!" The trackless snow softened Boyd's shout. "Once we rebuilt the whole world, but now we can't even melt a few glaciers." She gripped her daughter's shoulders, not roughly. "People got soft and forgot. Allel -- if I fail, you've got to carry on. Perhaps it will fall to you to take over, and lead our people to the Bridge. That's the truth of our world, the only truth. The only way to save ourselves that's within our power."

Allel returned her mother's fierce stare. "I understand, but..."

Boyd sneered: "But you want to ask the Shell dwellers what it's like living in a saucer." Her eyes were flat, impervious to the hard cold. Allel wondered how she and her mother had grown so far apart, becoming as symmetrical as opposing poles. The one pragmatic, the other -- a visionary? -- or a fool? Who was right? Perhaps that was a question without an answer--

She knew Boyd was trying to force her to grow up. But the Shell arced over them like a roof coated with its own ice. Could she give up all her dreams and become a creature of her mother?

"Listen," she said desperately. "I've thought of a way we can take the Bridge."