A man sentenced to 20 years in prison in the Monteforte prison, while working on creating toys for children, puts a note in a papier-mâché horse in which he claims to have been unjustly imprisoned and appeals to anyone who reads the message to get him out of captivity.

The horse, after alternating events, is collected in pieces in the hands of five schoolmates, Gianni, Andrea, Mario, Ugo and Nino, who find the note written by the prisoner.

By chance or by fate, even the members of the clan of prisoner 6211 are about to implement an escape plan to free their partner and take advantage of it.

The beautiful singer Amelia is also part of the criminal company, who, once they meet the boys, makes them believe that the life prisoner is her brother, so that the boys hasten the escape plan, freeing the gangster Jack Menotti.

The film sees the debut of Mario Girotti, then 12, later known as Terence Hill, in the role of Gianni, the orphan leader who pushes the team to the enterprise.