On his 16th birthday Mark's brother Thomas introduces him to the dark family secret and hands him the Chronicle of the Black Tower. A different world ruled by an eerie creature - the Gryphon. But how is the chronicle related to their father's death?

With Memo's help Mark reluctantly sets out to find his brother Thomas, who has disappeared in the world of the Black Tower. Meanwhile, Becky researches Mark's past and discovers a terrible secret.

Against his mother's will Mark tries to find a way back to the world of the Black Tower in order to save Memo. Meanwhile, Becky tries to find out if the contents of the chronicle really exist or if Mark is suffering from hallucinations.

Mark and Memo hatch out a plan to free Thomas. Becky doesn't suspect a thing. She is convinced that Mark is imagining everything. So is his mother, who wants him committed to a psychiatric ward. Will Mark manage to escape?

While Mark and Memo prepare for the arrival of the horned ones, Becky tries to convince Mark's mother that he is not suffering from delusions. But then fate takes a gruesome turn.

Mark's mother receives a shocking tip from Bräker about her husband's death. Mark and Memo face the ultimate horror in the tower world.