As the Marquez de Marquis helps the fledgling detectives Edwin and Charles further develop "haunting" skills, Charles begins to suspect that all is not what it seems with their mysterious tutor. Is he really after the killer of runaway kids or are his motives more sinister? And just as our intrepid duo closes the net on the suspected killer, Mad Hettie suddenly reappears to cast the boys' deductions in further doubt.