They've been massing for days, surfing the gusts of wind, rolling another few feet in the wake of every passing car, and now they start to converge in the north-west. It's almost dawn, and they're in twos and threes and more.
They know nothing's guaranteed. They know they aren't the first to run. Usually escape ends with capture and return, but they've all heard stories of the few who disappeared, and the reports that filtered back in the weeks afterward: bent wheels poking out of the river, dented husks left under a bridge to rust.
They drift closer. Cars drive past, but only a few, and they're quiet, curving gradually into existence, moving from a burr in one direction to a burr in the other. One has its headlights on, and they wait for it to pass, feeling the light as it slides across metal to cast gridded shadows. The next is louder, and it strums past in darkness.
It's good, for them, the dim murk: they can feel motion and make out distant lights. Later in the day they'll be blinded by the glare of sunshine as it reflects off their sides and dazzles them with its distortions. Even that won't be as bad as the fluorescent lights they're running from: days in the supermarket overwhelm, the fluoros whitewashing away any shapes, buzzing noisily over the rattles and clunks and vibrating echoes they use to find their way.
There's a sound in the distance, and they fall still. Footsteps.
"What was that?", someone says, and they don't know what it means but they get ready to let themselves roll backward, and it's a long time after the sound has faded away before they start to move again. They're almost at the edge of the world.
They don't know what comes next. They're creatures of the footpaths, of polished floors and smooth inclines: when they nudge the world-edge border it's jagged and unfriendly, soft, cumbersome. It bends beneath the sides of their wheels and they back away.
Except Cole. Cole's different. Even before he left, when he passed his nights chained in long rows with the rest of them, he was different. They barely recognise themselves as distinct entities, but everyone recognises Cole. He spent months as a Roamer, riding one of the homeless humans, carrying its bags of empty bottles in exchange for movement and protection; but then he began appearing back in the aisles, unpiloted, and disappearing again, and returning. They aren't sure where they're going, now, and they aren't sure how they'll get there, but they know that Cole's going to show them.
It's getting lighter. They stop moving, waiting for the stragglers to advance and draw them into a mass again. A few shift nervously, moving closer for comfort, nuzzling into each other to feel safe. There can't be long to wait now. Cole is motionless in front of them.
When they've all gathered as tightly as they can, he moves, away from them, away from the centre of the world. They listen, and watch. Rattle, clunk-rattle. He moves forward again.
It can't be that simple, can it? Surely there's more to the plan? But no: they see the day's first beams of sunlight glint off Cole's handle, and hear his wheels on the footpath grow silent as he crests the edge of the world, and rolls over into elsewhere.
He stops again, waiting.
It's almost an accident when the first of the others follow: a gust of wind that carries them forward before they can decide whether to brace against it or ride. Only two of them stay with it for long enough to cross the edge. A few seconds later another follows.
A horn blares. Distant music rises and falls, reminding them of the aisles, giving another few the courage to move forward.
By the time the cars have swelled to a constant whirr, and the sun's high enough to strike every one of them, another ten or twelve have nudged across the borderline, and it's become clear that that's it, that if they wait much longer it'll be too late.
On one side of the border, the mass lets itself fall backwards, rolling away from the edge. They'll wait to be collected. It won't take long. On the other side, Cole moves forward through the grass, slowly, and his companions struggle after him, further from safety and into something else.