The Mystery of the Empty Envelope

The mysterious house on Howard's End is a place people prefer to avoid. And it’s not without reason! Once, this mansion was home to a family of famous archaeologists, and one night, while their son Alexander Mercury was sleeping… 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 vanished, Einar even forbade him from going to school! But one day, a mysterious letter arrived addressed to Alexander. However, it mistakenly ended up in the mailbox of Rebecca and Joe, who moved to Howard's End just recently. But when Alex finally received the envelope, it contained nothing but a blank sheet of paper! Rebecca and Joe are sure it's not a coincidence. The investigation leads the kids to a system of mazes beneath London. Only too late do they realize that someone has been watching them for a long time…