Luna is an orphan living with her uncle and his traveling pony circus. She owns her own horse, Vagabond, an Arabian Barb who is her best friend in the world.

The circus has just arrived in Normantal, a town beset by terrible industrial pollution where the streets are empty and an eerie silence reigns. Her first morning in Normantal, Luna decides to take Vagabond out for a walk. She lets the horse wander at will and is rocked to sleep on Vagabond’s back. She wakes to find herself surrounded by a dense wall of smog, lost. Suddenly at the edge of the woods, a boy appears riding an old black horse. Fan is the boy’s name, and he guides Luna and Vagabond out of the fog bank. As they emerge, they find themselves standing in front of an old dilapidated building, the Proprex sponge factory.

Luna wakes the next morning to find Vagabond gone. While the police inspector is questioning all the circus employees, she slips off on a bike to try to get back to the factory, suspecting that Vagabond has returned there. She must find out why.

Also available, book 2 in the eco-mystery trilogy, La Piste Sauvage de Maître Hopila, in which Luna realizes that the horses of the pony circus may not be just ordinary horses . . .