A woman drives homeward and gunned down point blank at their garage. Afterwards, the husband who apparently is a Federal Judge sits so disoriented in front of his home after learning his wife's death. Colby and David brief Don of the crime scene.
At the FBI vicinity Megan, Don and Charlie works with cases that the judge handles that might relate to the murder but it will take days to accomplish. Charlie comes up with a mathematical solution using Spam emails as model to interpret his approach to reduce the suspects' list to people most likely to kill a judge's wife. The system leads them to the Duc Lu Phan, a gang leader of JFM (Just for Money), LA based Vietnamese gang. Don went to talk to judge Trelane to ask more questions that might help in the investigation. Colby and David went to interview Danny (Duc Lu Phan) and pressed information who amongst his people might be a possible suspect. Danny immediately gives the name of Raymond Hwong, the number 2 man of the gang. On the way out of Trelane's office, Don bumps with Nadine, a sexy prosecutor and who has casual interest on Don. They update each other's activity but suddenly Charlie came out of the elevator disrupting a possible love interest for Don and he feels so guilty.
Colby and David went JFM territory that went almost out of hand. David was so annoyed with Colby's attitude – interrogates like a military man (BTW, Colby is an ex-marine officer).
At the Eppes home, Charlie informs everyone about this Nadine. In between the conversation of Don's love life and the on going case Larry suddenly concludes that Nadine might be the next target as the prosecutor of that case. Charlie's face now filled with worry. David reports back to Don that Raymond may have the motive but does not have a nerve to do the hit. So it's back to zilch again. After that he diverts the conversation that he does not like Colby's attitude. Don just shrugs off because he thinks every new guy wanted to show off and wanted to do everything to fit "in" the team just like David a year ago. Colby joins the team reporting a news bit from LAPD dispatch database that LAPD responds to 5 domestic disturbance calls between May 2001 and June 2003 at Trelane's residence and did not file any charges. On two occasions as well Trelane ordered to vacate the premises. With this information they now repositioning that hit were really meant for Trelane and got the wife by mistake. Don confronts Trelane about these disturbances. Trelane admitted these domestic disputes but it does not mean he wanted his wife dead.
Megan and Charlie work more using different theorems to set criteria of the suspect. Charlie uses another approach and using report cards of his students for the past years as a model. But Megan was not convinced so he uses Origami as another model. Charlie relates that Origami have six basic folds – mountain, valley, diagonal, fold and unfold, reverse and turnover. It is a simple finite, imminently, quantifiable action. But infinite number of combination creates the possibility for an infinite number of forms. With this Charlie imposes to use same action – Risk, reward, consequences and certainty. In short, Charlie does not want them to completely rely on his system because human behavior is not that rational. It is simply a tool to help the team to use it much efficiently and gives Megan the end-result of his explanation – flower origami. Megan receives a call from David that a rumor is spreading that Raymond will hit back. Don went to warn Nadine about these rumors. Nadine then flirts with Don but Don is too preoccupied to notice. Colby and some FBI agents look for Raymond to prevent his plan. Unfortunately, he was nowhere to be found. At the Federal building, Don with Nadine escorting Danny Phan with Judge Trelane following, an unknown motorcyclist drives by and shoots randomly. Don got a good view and gunned down the suspect's motorcycle – and its Raymond Hwong. Hwong was brought down to the station for questioning. Apparently, Raymond was not aiming at the Judge but to Danny for giving his name as a possible suspect for the murder of Trelane's wife for pride's sake. So suspect is still at large and they are back to square once again. After the incident Don meets up with Nadine and in between the conversation Nadine wants Don to take his chances of having a relationship. At the CalSci, Megan, Charlie and Amita works with another system – Combinatorics, it is a branch of computer science. Larry then joins the group and meets Megan for the first time. With the combinatorics system they were able to distilled two possible suspects – Orson Hardee, a guy who he thinks got into jail because he wasn't given adequate representation. Orson was charged of killing Detective Josh Kalen in a drug deal in 1994. The second suspect is Lance Dolan. However, Lance Dolan has no connection or has ever been in Trelane's court. However, Charlie still insinuates that Lance's psych profiles are in line with killing Trelane's wife. Don was not convinced because he does not see any motives. But he stills agreed to work on the two focusing more on Hardee. Don paid a visit to Kalen's widow for safety precaution. At Eppes home, father and sons eat together and discusses Don's love life. Allan was happy that he risks his life for some girl. It's been a long time that Don showed interest to a girl. However, Don is not happy because he thinks anyone who got involve with him might end up like Allison Trelane and they grew quite.
A small break lead came from crimestopper line informing that Dolan is the killer of Allison Trelane. So to prove its validity Colby and David went to locate the crimestopper tip caller – Hector Machado, in some food establishment filching a waitress tip to give more details why give that tip. Don is still not convince about the system pointing Dolan as a more possible suspect and annoys that he is sending 4 agents to follow Dolan. Charlie with Megan backing him up, that like Math some expressions are hard to explain why Dolan is 99% sure to be the suspect. Charlie then uses another example where needles randomly falls into line of sheet and everything relates to PI and it is called as Buffon's needle. PI seemingly appears in quantum mechanics, relativity theory and number theorem and remained unanswered. Charlie concludes same goes with this Dolan. Don still dissuade when David joins the team informing them Hector Machado stabs Dolan last year and it is motive that Hector is setting up Dolan to get even. Larry in FBI office who came in with Charlie, take away Don from action, lecturing that it is okay to try on relationships using his physics knowledge. Don just smiled and said that he will keep that in mind. Hector cooperates with FBI in exchange for not involving him in the murder of Trelane's wife. He calls Stacey, the girlfriend to ask where might Dolan is hiding and Stacy hanged up and immediately placed a call to Dolan and informs that Hector gives him up. They trace the call and got him. Charlie at the CalSci office creates more equation to give him an answered why Dolan's name is turning up as a possible killer with no motives to kill the judge's wife while FBI is doing a raid at Dolan's home. It turns out that Hector introduces Dolan to Mrs. Kalen who ordered the Hit to Mrs. Trelane to let Trelane feel how to loose someone.
Allan and Charlie picks up Don at the FBI office to eat in a fancy restaurant but apparently the two does not know that Don have done a little consideration in their suggestion to try dating again.