In Little Seville, a fictional village near Madrid, nine eleven-year-old children, boys and girls, classmates at the same school and teammates in the school's seven-a-side football team, Soto Alto, swear never to part and to always play together everywhere. They secretly call themselves "The Footballers" and decide to solve problems and unravel the strange situations that come their way together.

The Inter-School Championship is ending, and Soto Alto is in danger of not only being relegated but also being disbanded as a team. The parents' association has stated that if Soto Alto falls to the B division, they will remove football from the activities and replace it with dance classes. The nine children, that is, the seven main players and the two substitutes, decide to do their best to win at least one of the three remaining matches. But just when they seem to be achieving their goal, the referee falls flat on the field and falls asleep. The match is interrupted, and when it resumes with a substitute referee, the game is lost for Soto Alto. The same happens in the second match, so the children, to avoid losing the final, decide to solve the mystery of the sleeping referees. Will they succeed, or will they get into dangerous adventures? Who do they suspect, and what will their investigation reveal?