Antonino is committed to a mental asylum where he is the passive witness of the time going by, a diary takes his moods, his physical sufferings.
He is unable to keep in touch with the other patients and feels a deep aversion to the rules of the asylum, he spends whole days alone, drawing multicolored butterflies.
After more than twenty years he is discharged and can savour the taste of freedom.
The maire assigns him a flat in a council house and while looking for it he meets his neighbor, Andrea, who helps him. This is an artist who is living an existential crisis which hinders him to create new works and to keep to the agreements with his manager, Harold, a cynic businessman dealing in the world of art.
Andrea has temporary been using the flat to store his buildings and so he offers his help to order it. This time spent next to Antonino rouses Andrea’s curiosity who, trough his sister, a lawyer, try to gather information about the illness of his neighbor. This new relationship focuses his attention and brings him to estrange completely from his professional responsibilities.
Reading Antonino’s diary, Andrea awakes his tenderness, he feels affection for that man who has taken part in his life by chance, he spends whole days listening to Antonino talking about his past.
Antonino brings his friends in the court of the asylum where he lived once and tells him about the story of a horse which was used to carry the dirty linen and whose passing was always anxiously awaited by all the patients, and tells him also about their frustration when they discover one day that a faster and newer machine has replaced their friend. The action of a doctor who help them to build a new horse is really providential. They will call him “Mario the Horse” Even though his manager keeps on insisting that he has to be present to an exhibition of his works, Andrea decides to send Antonino at his place, challenging Harold’s wrath who is forced by the circumstances to introduce Antonino to the critics…
The two lives mingle and proceed to a common destiny, Andrea wants to spring a surprise on the friend and start working to a project, that will prove to be the biggest of his life, the creation of an enormous, multicolored horse. Antonino receives the gift and, overcome by emotion, asks his friends to bring it out of the atelier. "Mario il cavallo" leave in search of freedom.