The day at primary school number 23 in the suburbs looked like it always did: bells ringing, laughter in the corridor, the sound of lockers being opened and quick conversations about homework. But for Mai, Igor and Lena, this day was about to become completely extraordinary. It all started during a physics lesson. Mr Szymczak brought a shiny new device to class, which he called a 'quantum portal simulator'. It looked a bit like a letterbox with lots of buttons and a screen flashing green. Mr Szymczak spread it out on the table and smiled mysteriously: - Today I'm going to show you something really special. But remember - don't approach the device without my permission! After a long, fascinating presentation, the break came. The class left the room, but Maja, Igor and Lena stayed for a while. Maja approached the device, looking at the flashing lights. - I wonder what will happen if we push this button? - she whispered to Igor and Lena. - 'We'd better not take any chances,' warned Lena, but Maja had already pressed the big blue button. The device began to buzz strangely, and whirling sparks appeared in the air. Suddenly all three of them felt as if they were falling for a moment and then fell on something soft. They opened their eyes. They were in a huge, shining dome, with a transparent ceiling through which distant stars and colourful nebulae could be seen. The air smelled of mint, and strange, glowing plants floated all around. - Where... are we? - Lena asked quietly. Then, from among the plants, emerged a tall robot on three legs, with two arms ending in grippers and a glowing, violet eye. It stopped in front of the children and with a metallic voice said: - Welcome, Explorers of Planet 3. Your presence has been recorded. Please identify yourself. The children looked at each other terrified and delighted at the same time. Suddenly, they heard approaching footsteps and a strange noise from the other end of the dome, and lights began to go out around them....