A cold day in January 2006. The police make a horrible discovery in the Swedish town of Hudiksvall: In one night, 18 people have been brutally murdered in the small town. The police suspect a madman is behind the bestial act. But when judge Birgitta Roslin hears the news, she instantly knows that her grandparents August and Britta Andrén are among the victims. And even more: Almost everybody killed somehow relates to her. She realizes that the police are following a wrong track and starts to investigate on her own. Her search leads Brigitta to China where she finds out about the cruel scheming of the leading elite.

The Viennese detective children Biggi, Patrick and Luke find a key in dragon form, and their curiosity is aroused. They realize that the sinister Lady Q is interested in opening the legendary moon palace and find the elixir which is believed that promises eternal youth. The Tigers must prevent that Lady Q enters into possession of the priceless liquid.