Conny Blank receives a call for help from a mermaid. She is to act as a mediator to warn the people of Wangerooge about an impending storm surge. Conny travels to the North Sea. However hard she tries, no one wants to believe her words. As predicted by the mermaid, the storm begins, bringing an even greater terror to Wangerooge than a storm alone ever could. A terror that has been lurking on the seabed for 600 years.