The 5 sleuths consist of siblings Betty and Pip, Harry and Daisy, and Freddy. Their group is completed by Buster, their dog. During their holidays, they are all together and solve criminal cases without fear! The 5 Sleuths are very happy that the holidays have arrived, giving them the opportunity to relax from their studies. An entomology conference, organized in Peterswood, brings a crowd of people to their area, many scientists, but also an escapee from prison. The marked man, with a horrible scar on his face, moves among them like a shadow. The children soon get involved in the search for him, without suspecting what awaits them…