In Little Seville, a fictional village near Madrid, nine eleven-year-olds, boys and girls, classmates at the same school and teammates in the school's seven-a-side soccer team, Soto Alto, vow never to separate and to play together always and everywhere. They are secretly called "The Soccer Balls" and they decide to solve the problems and figure out the strange situations that are presented to them all together.
The Interscholastic Championship is ending and Soto Alto is in danger of not only being relegated but also being eliminated as a team. The Parents' Association has stated that, if Soto Alto falls to the second division, it will remove football from the activities and start dance classes. The nine children, namely the seven main players and the two substitutes, decide to do their best to win at least one of the three remaining matches. But, where they seem to achieve their goal, the referee falls wide wide on the field and sleeps the good weather. The match is stopped and when it resumes after an hour with a substitute referee, the game is lost for Soto Alto. The same thing happens in the second match, so the kids, in order not to lose the final, decide to solve the mystery with the sleeping referees. Will they succeed or will they get involved in dangerous adventures? Who do they suspect and what will their investigation uncover?