Molecular chain tattoo down the back

Something in the caravan catches your eye on the way back: a battered school chemistry book left open on the stool, with a diagram pencilled across the flyleaf. A chain of carbon rings, drawn in a thin, careful hand, each hexagon closed off neat as a bolt head. Ray says the last lad who sketched on the flyleaf ran off with the Ferris wheel's takings and a fire-eater's wife. You decide it looks less like a stranger's bad joke and more like a map of something you have not yet been shown.

That night you sit in the cab of the dodgem track with a torch and copy it onto the back of an unused ticket, one ring at a time, until the chain runs off the edge of the paper. The generator dies at midnight and the field goes dark except for the little bulbs over the Hook-a-Duck. You trace the lines with your thumb and count: six rings, a bend, six more, like someone picking their way carefully along a fence.

In the morning the book is gone and Mrs Ostler is pinning your ticket above the till. "Thought you'd want that back," she says, and explains that the rings are a kind of sugar, which makes you laugh until you see she is not joking. You fold the ticket into your back pocket, and the fair rolls out for Carlisle with the chain still folded there, one ring for every mile.