Alex, whose singing career can't manage to succeed, accepts a strange job : to make a pensionner choir sing nursery rhymes. She finds out a bunch of out of control old people who dream of singing rock and roll music ! Her mission will be more complicated than expected...

Back to school for Ducobu, Léonie Gratin and Latouche. But this year, a major rival for Ducobu arrives at school: TGV, the king of cheating 3.0. While the financial situation of Saint-Potache becomes disastrous, the two dunces will have to unite their creativity to win a song contest and save their school.

When a father and son come face to face with two old sectarian psychopaths, running for their lives will be their only option where survival instinct and filial love will be pushed to the limit.