On Monday morning, Primary School No. 7 looked as usual: the voices of the children echoed in the corridors and the caretaker Mr Jan was unzipping his colourful jacket at the entrance. However, Simon immediately sensed that this day would be different. When he entered the classroom, he saw that an old brass bell, which he had never seen before, was lying on Mrs Eve's desk. The bell was decorated with mysterious marks resembling lightning bolts. The first lesson passed quietly, but as soon as Mrs Eve struck the bell, something unusual happened: for a moment, all the colours in the classroom began to move and the books jumped slightly on the desks. Simon looked puzzled at Zosia, who was sitting next to him. Her hair began to glow like neon lights. Philip, Simon's best friend, noticed that he could hear whispers from behind the wall, and Simon himself discovered that he can see through the walls as if they were made of fog! The children could not believe it. Was it possible that a simple bell had given them superpowers? When Ms Ewa left the classroom for a while, all three decided to test their new abilities. Zosia lit up the whole room with a flick of the wrist, Filip eavesdropped on the teachers' conversations in the corridor, and Szymon checked what was hiding behind the closed door of the teachers' room. Suddenly they heard the bell ring, this time different from usual - as if the bell itself wanted to warn them. They looked out of the window and saw that a cloaked figure had appeared in the schoolyard with a large, mysterious suitcase. The figure was looking straight at their window, and there was a strange gleam in its eyes. Simon felt a shudder. Could it be that someone else knows about their superpowers? What was hidden in the suitcase of the mysterious newcomer? The children looked at each other communicatively. They waited for the signal to set off for the schoolyard and discover what was behind this new mystery....