Mirette lives and works with her grandmother Mémé Gâteau who runs a Parisian boarding house frequented by circus performers. One night a mysterious guest named Bellini arrives.
While attending to her chores, Mirette discovers him in the courtyard, walking a tightrope fashioned from one of the washing lines. She is transfixed and becomes determined to learn. Undeterred by Bellini's refusal to teach her, she steals out to the courtyard each morning to learn by herself. She falls a great deal, yet continues despite her injuries. Soon she manages one singular crossing. Elated, she runs to tell the only person who could understand... Bellini. He surrenders and agrees to teach her. And so Mirette becomes a wire walker and a loyal friendship develops between the unlikely pair.
The arrival of Charlie Meyer, the infamous agent from London, brings song and merriment, but he recognises Bellini, and in so doing Mirette learns her mentor's secret - the world's greatest high wire walker has been left tormented by an accident and unable to perform at height. The next day Bellini disappears.
That evening crowds gather in the local square. Mirette follows to find out what is happening. A high wire has been set up. She spots Bellini as he steps out onto the rooftops. He is attempting to purge his demons. He tries to take the next step but freezes as fear takes hold. Mirette races to the opposite roof. Now standing on the edge, she too is scared. Yet to save her mentor, she must walk the high wire...