Emil And The Three Twins by Erich Kastner
Emil and the three twins? Three Twins? Yes, you read that correctly. Emil Tischbein has another adventure with his old friends the Professor, Gustav and Little Tuesday - this time by the sea. Of course, the detectives couldn't have an ordinary seaside holiday like other people - and when they become entangled with the mystery of the three acrobat twins and the wicked Herr Anders, it looks as if it's going to turn into a most extraordinary time for them all!