When the bodies of three female prostitutes are found in three different, but similarly staged locations, the CSIs realize they have a methodical serial killer on their hands. Russell notices that the bodies were staged in specific ways at each murder scene so that they matched up perfectly to engravings from a 16th century volume of Dante's Divine Comedy. Based on that, Russell posits that the killer plans to murder up to five more people, and that Brass' estranged daughter Ellie might be a target. After getting a preacher at a local church to fess up that he's been acting as a pimp for some of the victims, he helps the CSIs set up a sting to catch the killer, using Morgan as bait. As the undercover operation progresses, Brass and his ex-wife get a package delivered to them containing a flash drive. That flash drive contains footage of the killer torturing their daughter, Ellie, and Russell realizes that Morgan is in even more danger that they previously thought. Nick and Greg hurry to pull her from the operation, but they discover that's she has disappeared. The CSIs are left stunned, and the killer now has Morgan and Ellie as captives... Meanwhile, the CSIs are forced to allow John Merchiston, an investigative journalist, to follow them around for the week. Russell meets Merchiston at a Black Sabbath concert in Vegas, and immediately senses that the reporter will be a pain. However, Merchiston mentions a speech Russell gave from many years back, and ultimately ends up helping Russell figure out the murderer's MO.