Two fighters are in a boxing ring, sparring. One obviously gets the upper hand and corners the other fighter, punching him again and again. A trainer yells at him to stop, but he doesn't quit throwing punches until the trainer comes in the ring and physically separates the two. He asks if the loser, Munson, is alright, but the man collapses. At first, they think he's kidding, but then the trainer realizes that he doesn't have a pulse.
Charlie and Amita are playing poker alone, at Charlie's house. Amita wins the hand, and Charlie gets frustrated because he thought that he would win, because the percentages were in is favor. Amita tries to cheer him up by saying that Alan was out of town and they were alone. Charlie smiles and is about to kiss her when the doorbell rings and then Alan walks in. They ask him why he's in town, and Alan says he caught an earlier flight. Realizing he interrupted something, Alan offers to leave, but Amita says to join them for dinner, because Charlie always orders too much. Alan agrees, completely missing the glare Charlie sends his way.
David shows up at the gym, having received a call from LAPD. The lead detective tells him that the suspect dropped his name. When David hears the fighter's name, Ben Ellis, he is obviously shaken. He tells the detective he knew Ben a long time ago. David asks why the victim's death is being treated as a possible homicide, and he is told that the ME thinks there might have been poison in his system. He asks why Ben is a suspect, and finds out that another fighter, Octavio Lopez, died in the ring with Ben six months ago.
David goes to talk to Ben, and he swears he didn't kill Munson or Lopez. David is skeptical, especially when the detective comes back to say that someone heard Ben threaten the victim that day. David enlists Charlie and Amita's help to narrow down the list of suspects, and they find that the only thing connecting the two dead fighters is that they were both fighters. They also realize that with the two of them dead, Ben moves up in the ratings.
However, Charlie's concentration is soon taken away from the case because he is practicing poker to take Larry's place in a Texas Hold 'Em competition. Larry has won this part of the tournament 5 years in a row, and Charlie wants to make sure his seat is waiting for him when he comes back. One of Cal-Sci's bio-chemists, Professor Stanley Novich, desperately wants Larry's spot at the tournament, and does everything in his power to psyche Charlie out as he prepares to play. He even goes so far as to "skunk" Charlie's office, forcing him to have all of his meeting at his house, and use Amita's laptop for his work.
Meanwhile, the test results for Munson and Lopez come back, and it is discovered that they were both killed by a poison called 1080, a form of sodium flouroacetate. The drug causes cardiac arrest. Claudia in the FBI morgue tells David that Munson had an allergic reaction to it in his mouth, but all of the water bottles in the gym come back negative for the poison. One thing that doesn't come back negative is Ben's locker and gym bag. A warrant is sworn out for his arrest on both counts of murder. David is so mad at him that he takes Colby and decides to arrest him himself. However, Ben gives them the slip and escapes custody.
Don is frustrated that David is being so affected by this case, and asks if he needs to step away. David says no, but opens up to Megan about why he and Ben are so mad at each other. It turns out that when David, Ben, and Earl were kids, Ben and Earl went to a burger joint where Earl's girlfriend worked. Ben started a fight with a guy and in the process, a gun is pulled and Earl was killed. Megan responds, "And you blame Ben?" "So did the State of New York," he says. Ben served two years in youth detention.
When Charlie figures out how to find Ben by using his call log, David and Colby take a team to pick him up. Ben pushes David, but Colby backs him up and Ben is taken into custody. During his questioning, Ben says that he's not the only one who could benefit from the deaths, but David doesn't want to hear it. He stalks out, and Don goes to talk to him. Don tells him about a time when he put the wrong man in prison for ten years. He says not a day goes by when that doesn't come to mind, so David should make sure of Ben's guilt before he throws away the key.
That conversation gets David thinking, and he gives Claudia a sample of Ben's DNA to check against the DNA on the gym bag. If it's not his, it was planted. She calls him back, and shows him that the test results are negative-it's not Ben's bag…he was framed.
With Ben cleared, the team is back to square one, until Ben tells them that rankings aren't the only things in play for the title. Alston, the head of the league, ultimately decides who fights who. With this new information, Charlie and Amita head back to the math and come up with some startling results. They realize that Alston has not been playing fair-he has been pitting one particular fighter, Bainsworth, against people who were sure to lose to him so he could make it to the final fight against Tino Alvez. That fight is supposed to bring loads of money in through Pay-Per-View, and would help bring the league out of debt. The fight had to happen between Bainsworth and Alva, or Pay-Per-View could pull their support. The team realizes that Alston had the two fighters killed because they may have been able to beat Bainsworth.
Meanwhile, with Ben out of jail, he's next in line to fight Bainsworth. They realize he's in danger, so David and Colby go off to warn him. Megan and Claudia frantically search for the means by which the poison was delivered, and finally figure out that it's in the mouthpiece. Megan tries to call David, but he doesn't answer his phone.
David and Colby have technicians check all of the water bottles in the gym and finally let Ben go fight. Ben puts his mouthpiece in, and wins the fight in the first round. David confronts Alston, telling him they found the mouthpiece, and he was under arrest. Ben will now go to the championship against Alva. Ben and David put the past behind them, and Ben admits to David that Earl was really the one who started the fight that day, and he was just following his lawyer's advice when he said he did. The two leave each other on good terms.
The episode ends as Charlie and Stanley are the last two people left in the poker tournament. Between Alan, Megan, and some security cameras, Charlie has figured out Stanley's tell. He had some of Alan's friends come in the middle of the night and drywall Stanley's office door shut, then paint it the same color as the wall, effectively making his office disappear. Then, he watched what Stanley did when he was agitated. Thanks to that practical joke, Charlie notices Stanley's tell and beats him in the last hand, securing Larry's spot in next year's tournament.