The Coonskin Cap

S4, E1: Policewoman Heather Davey is impossibly strangled to death inside an empty gymnasium. Two young women have also been murdered in almost identical circumstances, and fears are growing that the killer will strike again. Jonathan is promptly recruited to accelerate the enquiry, his only clue to the killer's identity is the macabre shadow of a man wearing a Davy Crockett hat witnessed lurking near the scene of the murders.