The CSIs have a serial killer on their hands when a drug dealer lounging at a hotel cabana is killed during an eclipse and the ligature marks around his throat resemble that of a recent murder victim in the area. The investigation leads the CSIs to a Mario Montero, whose DNA was found at the crime scene, but the results mysteriously reveal that he was taking wolf hormones stolen from the victim. Further evidence links a missing employee ID card to a pool boy, who has cuts on his hands and was working at the pool when the murder took place.
The earlier victim, Diana Long, was killed around midnight and was found in her apartment by a delivery guy. Long lived her life on her computer, and right before she was murdered, was chatting with a Nicholas Pike. Pike works in the nightclub business and was interested in meeting someone other than a model/actress, so he turned to the internet. Things get even more complicated when Montero is attacked the same way as the other victims, but he survives, thanks to his pet wolf, which scared off his assailant. While going through the lounge chairs at the hotel, Natalia finds traces of a lotion used by people with an allergic reaction from the sun, causing them to break out in hives and blisters. There could be a connection: this killer killed his victims at night. In the end, the CSIs discover that Nicholas Pike, who is allergic to the sun, framed the pool boy by placing his blood at the crime scenes and set out to randomly kill people who took advantage of being able to be out in the sun when he couldn't. In the midst of all this, Ryan is finally reinstated as a CSI.
[Edit]