As Halloween descends on Sin City, the CSIs investigate when a creepy mannequin prop inside a popular haunted house turns out to be a real dead body. Also, Catherine enlists the help of Folsom to search for her friend who disappeared.

When wrongly accused former suspect Gene Farrow enters the Crime Lab covered in blood, wielding a cleaver and looking for Allie Rajan, the CSI team investigates his peculiar story about a macabre party with a fatal ending.