A prison guard at Carson State Penitentiary has just been murdered by a prison shank. Outside of prison. It’s mysterious circumstances, but Walton Parcell was not just any prison guard. He had aspirations of being a detective and was going to community college for criminology. Though he is outside a jewelry store there was no robbery, although there was one earlier in the month.
Though Grace is handing out wedding invitations, she’s also used Walton’s call history to track down a girlfriend, Shelly, and Rigsby has been given a list of former Carson inmates in the area to interview on their whereabouts last night — including his father. Steve Rigsby is just as described in an earlier episode, and worse. He’s very abusive in his language towards Rigsby, who hurriedly leaves.
Lisbon and Jane interview Shelly, who had been dating Walton for a couple of months. They’d last had a date a couple of months ago, but otherwise she seems unhelpful. Cho and Grace are at the prison talking with the warden, Walton’s boss, who has a rather dim view of Walton’s ambitions to be a detective.
Walton had been working with his professor on a case to have one of the Carson inmates transferred, so Jane and Lisbon visit the professor in her classroom. When she tries to make a point about the human brain being inefficient and “not a computer,” Jane shows her up by being able to tell everyone that May 31, 1976 was a Monday, and that his brain is a computer. He compares the mind to a dark closet that the average person throws things into, willy nilly. He invites each of the students to search their minds for anything that would be connected to Walton and the case he was building. Between two students and the teacher, they managed to come up with a male with white gang tattoos, from Fontana, named Marcus.
Now working on the premise that someone in the prison system with that description had a man on the inside, they find Marcus Lansdale, who as it turns out is the big kahuna on the cellblock. He claims that if he wanted a guard dead, the guard would be found in the broom closet on the block. Jane walks out once he has all the info he needs before Lisbon is ready, and they return to visit Shelly. Shelly is Lansdale’s sister.
Shelly’s thing with Walton started as a plan to find out what he was up to in the case to transfer Lansdale, but she eventually fell for him and told her brother she wasn’t going to do it anymore. Now she also won’t give a statement against him, but since her alibi for the night of the murder checks out there isn’t a whole lot the CBI can use her for.
The next day while Cho and Jane head back to the prison, Rigsby takes Grace with him to see his father again, who had claimed he could catch the killer in ten minutes during the first visit. He takes them to find a woman named Laine Hamilton, aka Rocket — who tries to run. Laine points the finger at a guy named Butch Carmen who has a meth lab set up outside of town. Rigsby and Grace bust him, and take him in.
Meanwhile, Cho leaves Jane at the prison, and Jane is slowly working out his plan and asks to speak to some trustees — inmates who are trusted by the guards and therefore have special privileges. He picks out two, Jorge and Nick, who show him around the place. When Jane asks about Lansdale and his hold on the block, Nick answers curtly, “I know to mind my own business.”
Carmen doesn’t know Walton, and as it turns out, meth was not the only line of business he was in — he has a stash of smuggled (untaxed) cigarettes. Here Rigsby puts two and two together and figures out that his father has used him to take down a rival. He confronts him but falters when his father shows that he isn't afraid of his son. Rigsby Senior invites his son to take a swing but shows the knife at his belt and warns him — he doesn’t do fist fights. Rigsby walks away.
Jane spreads word that Nick is a snitch and manages to get him in trouble. News gets back to Lansdale, who plans to take things into his own hands and take Nick out for snitching, but of course it’s a set up. Cho is waiting in the cell instead of Nick, and Lansdale is taken out. Nick has also disappeared from the night shift in the laundry room.
Jane, Lisbon, and the cops are waiting for the laundry truck as it leaves the prison, and they catch Nick redhanded in the back. Nick orchestrated the earlier jewelry store robbery so that he would have some startup cash when he got out of prison in six months, and bribed the truck driver with a cut for getting him in and out of prison undetected. When he went out a second time, Parcell had seen him outside the store, and pursued him. To keep his secret, Nick killed him.
With the case closed, Rigsby is back at his father’s place, burning his stash of untaxed cigarettes. They duke it out, fist fight, and Rigsby gets his father to the ground. Before he can do any lasting damage, he offers him a hand up. His father accepts, but he reflects, “I should have used the knife.” They part ways, and then back at headquarters, Rigsby tells Grace that he won’t be at her wedding because he’s still in love with her and can’t watch her marry another man.