The secret of an empty envelope

People prefer to bypass the mysterious house on Howard-End Street. And no accident! Once upon a time, a family of famous archaeologists lived in this mansion, and one night, while their son Alexander Mercurius was asleep ... they disappeared. There are rumors that Alexander still lives in that house under the care of the old butler Einar Stein. After Alex’s parents disappeared, Einar even forbade him to go to school! But once a mysterious letter came to Alexander. True, by mistake, it got into the mailbox to Rebecca and Joe, who moved to Howard-end very, not. But only when Alex finally received an envelope, it contained just a blank sheet of paper! Rebecca and Joe are sure that this is not an accident. The investigation leads the guys to the labyrinth system near London. Only too late do they understand that someone has been following them for a long time ...
For secondary school age