During the police marathon in Las Vegas, Grissom sees a runner outside the road and drives his car to the place, leaving Catherine alone. He finds a police officer dead. Dr. Robbins find that the victim was in excellent shape, but he had ingested two substances that combined killed him. Meanwhile, Sara, Warrick and Det. Louis Vartann investigate the murder of officers Manny Senteno and Patricia Fielding in a hotel room. Warrick's first impression is that might be a murder-suicide case. Soon they find fingerprints of the police officer Lydia Lopez and learn that she was lodged in the next-door room. When they look inside the room, it is completely trashed. Lydia says that she had sex with a Manny once a year during the marathon and she believes that her husband Archie Lopez might have followed her and trashed her room, but would never kill Manny and Patricia.

The death of a casino hotel guest is tied to an unlikely sexual encounter with a married woman in the room next to his, and a cat and a parrot may hold the clues of their owners' apparent double homicide.