Martin and Mercury - Alien in the Class

There is a new student in the happiest class on earth, who claims his name is Mercury. He has the picture of a planet on his pencil case, he drums Morse codes on his desk, can count as a robot and insists to have his own space station. It seems just too suspicious for Martin who starts to investigate... He can find out the truth about Mercury, but things don't end here. How can he keep everyone happy in the happiest class?

Children's fiction. A novel.