Russell, Morgan, and Greg are mystified when they discover the body of Peter Coe, who was killed inside an empty hotel elevator by a slash wound to his neck. After examining the wound, Hodges determines that the slash wound was caused by a thrown playing card, and a quick search of the elevator shaft reveals a bloody Ace of Spades. Meanwhile, Nick and Sara discover the body of a Trent Aldridge, who was tied to a bed and force-fed seven raw chicken hearts - the 7 of Hearts. The CSIs are convinced that the cases are related, given that both men were prominent in the poker world, and that they might be dealing with an intelligent serial killer. After going over old murder cases with similar victim deaths, Nick discovers Ed Ficelli's murder case and makes the connection. Ficelli was a pit boss at the local casino that hosts big poker tournaments and Finlay discovers that he was killed by an overdose of heroin laced with clover. Combining the track mark pattern with the clover, they find the 4 of Clubs. Signs point to local magician and financial backer Dr. Jimmy as the killer, but they can't tie him to any of the other victims. The team finds one final victim, Ava Rendell, who was decapitated with an axe similar to the one depicted in the King of Diamonds playing card. Greg digs deep into past poker tournaments to find a connection between the victims, and he eventually discovers that Coe, Aldridge, Ficelli, and Ava's father were all involved with a scam that bankrupted another famous player, Bo Mattison. After running a DNA scan on the axe used to kill Ava, they find DNA belonging to a female relative of Bo's: his daughter, Katy Hill, who is also Dr. Jimmy's assistant. Morgan finds Katy and is forced to shoot her when she pulls a pistol, and Russell and the rest of the CSIs are able to locate Dr. Jimmy, the intended fifth victim.