Leon is in an apartment with a young woman, Candi, throwing him on the bed and kissing him. She takes out a pair of handcuffs and cuffs him to the bedframe. As soon as he's secured, a Nigerian and his henchman come in and demand their money. Candi collects her money for turning Leon in and walks out. As the Nigerian prepares to cut out Leon's intestines, Leon warns him that they should leave while they can. Reese and Bear burst in and Reese makes short work of the Nigerians. He tells Finch that he's saved Leon, who wants to go a drink. Finch tells Reese that they have a new Number in Atlantic City and tells him to leave immediately.
Reese arrives at the Venus Casino and Finch explains that the Number is Lou Mitchell, a retired watch repairman. His wife died six months ago and he has no children. Lou doesn't have a cell phone and almost no digital footprint. Reese walks past the man as he gambles and loses at the baccarat table, and Lou leaves for the night with Reese following him.
The next day, Reese follows Lou to a pharmacy and doesn't spot any threats. Finch has to hack Lou's bank and confirms that the man is living on his Social Security. Reese figures that he's in debt to a loan shark, and notices that someone has broken Lou's fingers in the past. Lou goes to a diner and the waitress, Kelly, greets him by name. She tells Lou that a casino guy, Darien Makris, is buying the diner to tear it down for parking space. Meanwhile, Finch tells Reese that he's found a wedding announcement for Lou in 1972. Lou's wife Marilyn had a friend give her away and Finch figures that her parents didn't approve of her marrying Lou. Reese tells Finch that he'll have Carter look into it while Finch continues running checks on the man's finances.
Carter checks with Detective Szymanski, who confirms that Lou was connected to the Jersey City mob in the 1970s. Those men are long gone, but the new ones are even worse and are heavily involved with narcotics. Carter has Terney run a background check on Detective Stiles. Cal comes in to invite Carter to quick. She wants to think about it and Cal says that he's already made reservations for the coming weekend. Carter agrees and asks him to help her look into the Venus Casino.
Reese follows Lou back to the casino and Finch is surprised to learn that Lou has just forked over $1,500. He wants to access Lou's loyalty card to figure out his gambling habits, and hacks the casino computer through their online blackjack games. Finch slips malware into the computer system, while Reese notices Makris has come over to bet against Lou. Makris is a local celebrity and Carter has been looking into him for cocaine distribution. Meanwhile, Lou loses and Makris invites him to have a free spin at the wheel. When Lou swipes his card, Finch accesses the man's gambling history and learns that he's lost $2,000 a day for the last six months.
Back at the library, Reese and Finch try to work out where the money is coming from. Reese suggests that Lou may be a retired mobster, but Finch refuses to believe that Lou could hurt anyone.
At the station, Carter is surprised to see IAB bring Szymanski in. Szymanski insists that he's been framed and the IAB officer, Ginsberg, will only say that someone in Narcotics got a tip from a CI that turned out to be true. As they lead Szymasnki away, he tells Carter that he was supposed to testify that day and someone is dirtying him up to keep him off the stand.
At the courthouse, ADA Melinda Wright tells the judge that Russian mobster Peter Yogorov was supposed to be on trial for murder. Wright figures that Yogorov planted the evidence against Szymanski to keep him from testifying and asks for a continuance. Meanwhile, Simmons approaches Yogorov as the bailiff leads him out and takes command of the prisoner. The HR man informs Yogorov that the primary witness against him won't be testifying and leads him out. He takes Yogorov to meet with Quinn, who explains that Szymanski's testimony is now under scrutiny. Quinn offers to keep Yogorov and his brother out of prison in return for cash. Yogorov, who knows all about HR, agrees as long as Quinn can get him freed.
Finch takes up tailing Lou back to the pharmacy. Meanwhile, Reese visits with some of the local crooks in Jersey City and confirms that all of Lou's mob buddies are dead of natural causes. None of them have heard that Lou is in debt to loan sharks. Finch notices that several of the gamblers from the casino are frequenting the pharmacy, and points out that Lou picked up a prescription two days in a row. He tells Reese that he'll get someone to do some digging and Reese heads out to do some digging of his own.
Finch calls Leon and has him do some checking. Leon confirms that the Pharmacy is owned by Lionwood Enterprises, a shell company with only one confirmed partner: Darien Makris. Lou comes over and tells Finch to introduce himself if he's going to tail him. He has Finch sit down with him and asks why he's been following him. Finch gives him an alias and claims that he's with the IRS and looking into the Venus Casino. He asks Lou where he's getting his money, and Lou offers to play him baccarat for answers. Much to Finch's surprise, Lou deals and wins the first hand and asks why Finch thinks he needs help. Lou keeps dealing and winning, and Finch checks his sleeves. He asks Lou to let him help him, but Lou refuses and walks away. As he leaves, he takes Finch's car keys that he's pickpocket and tosses them in the lobster tank so that Finch can't follow him.
Reese picks Lou up at the casino again and realizes that he lost Finch. He checks with Finch, who is back at the library, and Finch figures that Lou is throwing the games. As Makris comes over to talk with Lou, Finch checks on the people from the gambler and realizes that they've been losing money at the same rate as Lou. Finch figures that Makris is using senior citizens to launder his drug money. Reese spots one man tossing a prescription bottle into a garbage can. He goes over to check it out and discovers there are dozens of similar bottles inside. Reese figures that Makris is forcing them to run money for him, and realizes that Lou's Number came up because Lou is skimming money from Makris.
At the precinct house, Carter and Cal watch as IAB interrogates Szymanski. Carter asks if Cal knows who made the call from Narcotics, and he admits that he did it. He refuses to tell her the name of his CI, but insists that the evidence speaks for itself. She walks out and Terney tries to talk to her about Stills, but she says that she'll have to talk later. Carter goes to Fusco and asks if he's heard anything about Cal. Fusco warns her that HR isn't gone, but admits that he doesn't have anything on Cal. He warns Carter that if she follows the money then she may not be happy with what she learns.
In Jersey City, Lou takes off and Makris' man Eric draws a gun on him and says they know he's been skimming. Reese takes out Eric and his fellow thug, and Lou realizes that he's with Finch. They meet with Finch and Lou explains that he cheated at cards at the casino to pay for an expensive stem cell treatment for his wife. Makris got hold of a list of old card sharps, saw Lou's name on the list, and put him to work laundering money. Finch insists that he won't let Makris comes after him and gives him ticket and money to keep him comfortable in Chicago. Lou refuses to leave his wife's grave behind and Finch tells him that he has to move on. The card shark realizes that Finch lost someone as well, and explains that 40 years ago the mob caught him sharping, broke his fingers, and left him for dead. Marilyn, working as a waitress, found him in a dumpster and nursed him back to health. Thanks to her, Lou gave up gambling and became a watch repairman. Finch tells Lou that Lou would want him to save himself, and he reluctantly gets on the bus. As he goes, Finch explains that Reese will make it appear that Lou died.
Back at the library, Finch warns Reese that Makris won't stop looking for Lou. He admits that they don't have the evidence to put Makris in prison. When Reese wonders how they can get the real financial figures that will convict Makris, Finch says that they need a distraction.
Finch gets a job at the casino as a cashier and sets up Leon as a playboy millionaire. Makris greets him and Leon starts gambling with big money. Leon puts on a show to keep Makris and his men watching him, while Reese steals a security key card from a guard. He slips it to Finch, who goes to security room and hacks into the computer system. Reese returns to the casino and discovers that Lou is back at the tables, gambling and winning with all of the money that he's skimmed over the years. He tells Finch and then calls Lou out into the hallway to talk to Finch on the phone. Finch warns Lou that they can't download the files and protect Lou at the same time, but Lou insists that he's going to keep his promise to Marilyn not to throw his life away. He plans to win back every dollar that he helped Makris make. Finch agrees and says that he thinks that they can take Makris for more than just what Lou has lost. However, he warns Lou that he'll have to bet big to win big and stakes him.
Lou returns to the casino and starts gambling with the $2 million that Finch has staked him. A crowd gathers as Lou wins and keeps winning. Finch tells Reese to keep an eye on Makris and then goes back to work loading downloading the documents.
Makris finally notices all of the people cheering Lou on and goes over to see what's happening. He's shocked to see the old man and starts to make a call to Eric. Reese draws a gun on him and tells Makris that Eric is heading to Vermont in the trunk of a car. Finch downloads the books and emails them to Reese, and Reese tells Makris to let Lou play or the files will go to the FBI and the IRS.
Lou continues playing, cheating as necessary to win. He finally closes out with just over $20 million and asks the cashier to deposit it into his account. Makris has no choice but to approve the transaction. As Reese and Lou leave, Reese tries to contact Finch. Makris and his men come out and tell Reese that they spotted and captured Finch and Leon, and one of his men knocks Reese out.
Makris and his men take all four captives to a laundry room beneath the casino. The mobster promises that he's going to show the old man that he's a loser. He takes out a gun, puts one bullet in it, and spins the chamber. Makris then forces Lou to hold it, points it at Reese, and pulls the trigger. Nothing happens and Makris aims the gun at Leon and pulls the trigger. The hammer lands on an empty chamber and Makris points the gun at Finch. Finch says that sometimes luck just runs out, and Reese kicks the table into Makris. He smashes the chair, frees himself, and takes out Makris' thugs. Makris tries to shoot him and discovers that the gun is empty. Lou reveals that he slipped the bullet out and punches Makris unconscious.
The next morning, the police take Makris and his men away. Leon and Reese watch and Leon complains about losing Candi. He promises to turn over a new leaf and start protecting people like Reese and Finch. Reese congratulates him... and demands that he hand over the $100,000 chip that he stole.
At the station, Carter comes in and tells Fusco and Terney that the marked bills that IAB found at Szymanski's place came from a bodega that Elias owned. She figures that it should be enough to get Szymanski out on bail and testify against the Yogorovs. As she walks away, she gets a call from Cal. Fusco warns her that someone has it out Szymanski and tells her to watch her back. Carter considers the call for a moment and then ignores it.
Lou and Finch go to the diner and Finch points out that the police are holding the money as evidence. He tells Lou that he knows what he planned to use the money for: a diner. Finch points out a photo of a younger Lou and Marilyn on the wall, and Lou explains that he and his wife considered it a second home. Now that Makris is out of the picture, Lou figures that the diner is safe. Finch points out that someone else could buy it, and then gives Lou the $2 million watch that Reese received from Logan Pierce. He asks if Lou would be interested in repairing it for a suitable fee. Lou thanks him, mistakenly assuming that the woman Finch lost was dead. He quickly realizes that the woman is still alive and tells him to go to her while he still has time.
Reese is playing with Bear at the library when Finch comes in. He's surprised to learn that Reese was listening in, and Reese tells Finch that he did what he had to, to keep the woman safe. Finch admits that if he returned to his old life, it would cost Grace her life. Reese says that he understands that some people don't get to grow old with the people they love, and Finch says that he'll grow old with her from afar. He then sits down at his computer and brings up an old photo of him and Grace together.
Yogorov is thrown back in jail and calls Simmons to tell him that the deal is off. Simmons tells him that he should have more faith.
Quinn meets with Wright and Szymanski in his office, claiming that the mayor wants him keeping up on the case. Wright insists that they're not going to let the Yogorovs stop them. Quinn takes out a gun, shoots them both dead, and calls in Terney to make sure their story about a shooter is ready. He then has Terney shoot him in the shoulder to make their story look convincing.