Immediately after a major poker win at a hotel casino, the poker room lights go out and the casino is robbed of over a million dollars in chips. However, when the police catch up to the presumed robber on his motorcycle, the robber unexpectedly dies and they find that he only carried counterfeit money and chips. The CSIs are called in to investigate the murder and robbery. Dr. Robbins determines the robber died of an allergic reaction to a toxin that was injected in his system by an unknown assailant. When security footage indicates that there was a second robber dressed identically to the first, the CSIs realize their body is the decoy and the real killer is still out there.Dr. Robbins concludes that the toxin came from a rare snake venom, and the CSIs use that information to locate another suspect - a valet who worked at the casino, but was shot to death in his apartment. Evidence at that crime scene leads Greg and Morgan to a casino mechanic, Ryan Borden, who reveals to them that was son has been kidnapped by the casino robbers and that he played a part in the robbery to save him. The CSIs initially buy his story, but DNA evidence from the casino crime scene - specifically, orange sweat caused by a specific medication - indicates that Ryan is lying to them, and that he masterminded the whole operation. He killed three people who helped him in the heist, then attempted to frame the deceased victims in order to make a clean getaway with his son.