"Why should I come?"

Without looking back, Boyd said simply: "Because if you don't I'll break your rubbish neck."

Allel looked back ruefully at her home, where the fires of the recent night were still burning. Then she clutched her crumpled shirt closed against the wind and followed her mother.

The breeze lifted the abandoned balloon; its final flight ended in the ruins of the lamp, where it began to burn fitfully.

The Sun wove its helical web around the world.

When night fell Boyd and Allel sheltered beneath a wild cow-tree. In silence, they drank from its milk nipples and broiled slices of meat fruit over a small fire. Boyd slept sternly beneath her quilted coat. Allel shivered in her thin garments, and burrowed into a nest of leaves. She peered up sourly at the Shell's seamless dark, picking out clustered fires.

In the morning she stuffed leaves inside her clothes and fashioned herself a rough cap of cow-tree bark.

After some days of this the frost grew more persistent, until their feet crunched over thin ice. Light snow fell. They passed a few abandoned settlements; even the hardy cow-trees grew sparse here.

A blizzard closed around them like a white mouth. They staggered up to the milkless corpse of a cow-tree. Allel stared at the shrunken nipples and withered fruit. Boyd laughed at her, her eyelids sprinkled with snowflakes. "Comes as a shock, doesn't it? A dead cow-tree. We were given a world filled with beautiful buildings, and cow-trees to feed and clothe us like mothers. A home safe from the Xeelee.

"But the world's old and falling apart. The Sun seems to be failing. Ice has covered the cities and frozen the milk in the cow-trees. We trudge through the snow." She began digging into the snow packed against the dry wood. "Come on. We'll let this lot blow itself out. The snow will keep you warm."

As she worked, Allel considered a changeless life of endless summer. What would there be to do all day? Her bare fingers grew numb.

When the storm blew over they continued the journey. With the Shell like a map over them it was impossible to get lost, and at last they came to the lip of a great natural bowl. Snow pooled around the low buildings of the City, which were sprinkled in two matching crescents.

Allel, used to crude teepees of cow-tree bark, touched walls that were as smooth as skin. But the interiors were cold and jumbled, and snow drifted waist-deep in the avenues.

Lifting heavy legs out of the snow, they forced their way to the common center of the City's twin crescents. Here was a small cylindrical building, no more than three paces across. Allel helped her mother scrape snow from the door. Boyd blew on damp fingers. "Go ahead," she said slyly. "You first." Allel pushed through the light door--