The three !!! spend the Whitsun vacations with Kim's godmother Clarissa at the beautiful Schiertal Lake. Actually Kim, Franzi and Marie just want to relax there, but soon after their arrival they are in the middle of their 20th criminal case. Shortly after Kim's godmother's summer house was broken into, a mysterious man shows up at her house and threatens her. And Clarissa seems to know this guy as well, who the three detectives are soon able to unmask as an unscrupulous gangster.