Monk is at home making breakfast and watching a news broadcast about an escaped prisoner, Joe Endicott, who murdered a woman. Monk hears a noise in the next room and goes for his gun but is unable to get the storage box open. He clubs the intruder over the head with the box and discovers it's Joe Endicott. However, "Joe" says that he's actually Monk's half-brother, Jack Monk Jr. He's surprised their dad never told Monk about him. Jack describes facts about their father and convinces Monk he is who he says. He also explains that he was using the name "Joe Endicott" when he was selling stolen cars, which is how he ended up in prison. He admits that he escaped but that he didn't kill the woman, a social worker named Lindsey Bishop.
After a shower and a meal, Jack asks Monk to help him clear him of the murder charge. He explains that Lindsey helped the prisoners with their appeals and everyone loved her, and if he goes back to prison then someone will kill her for revenge. He promises he'll go back to prison once Monk finds the real murderer. Monk agrees to hear him out and Jack explains that he was put in a cell by himself and dug an escape tunnel into the sewers. He saw the car outside, found Lindsey's corpse, and tried to call 911 on her cell phone. A guard spotted him and Jack tossed down the phone and ran. Monk doesn't believe it and prepares to call the police, but Jack asks him to talk to his mother Darlene. Jack calls her and Darlene begs Monk for help. She starts crying and Monk can't bring himself to turn her down.
Monk and Jack go to the prison and Monk looks around while Stottlemeyer and his team are there. When Stottlemeyer wonders who Jack is, Monk claims he's his pen pal from Canada. The warden and the prison guard who fired at Jack, Dennis Reese, arrive, and they both are eager to find Jack. When questioned, Reese says he didn't see Jack kill Lindsey. The warden, Tom Bennett, has the murder weapon: a piece of sterling silverware with the letters "GOSF" on it. The search team arrives with their dogs, which pick up Jack's scent. Monk quickly gets Jack away and they go to a diner. Jack recognizes the waitress as a Paraguayan and flirts with her. Monk is satisfied that Jack is innocent and wonders who knew Jack was escaping. Jack says his cellmate Shiv knew, and Monk points out that earlier Jack said he didn't have a roommate. Monk begins to realize his half-brother is a chronic liar, and Jack explains that he knocked out Shiv and "borrowed" his escape route. Monk says they need to talk to Shiv but Jack protests, saying if they do then Shiv will realize Jack is involved.
The next step is going to Lindsey's home, where Jack breaks out into fake tears to convince the superintendent to let them in. Monk searches for clue while Jack steals Lindsey's money, until Monk tells him to stop. Jack notices lousy photos of Lindsey on the wall and Monk realizes she never would have hung them herself. Someone took down the photos and put up Lindsey's discards.
That night, Jack is watching an old movie while Monk tries to sleep. Monk finally goes out and the two brothers bond over the movie, one of their dad's favorites. Monk notices that Jack is reading a book about Paraguay. After vacuuming the popcorn crumbs, Monk and Jack share a bowl of cinnamon-flavored popcorn and discuss if Jack was a terrible father. However, when Jack says their father wasn't the same since Jack's mother died, Monk realizes the woman on the phone earlier wasn't Jack's mother, and Jack has lied again.
Monk calls Stottlemeyer to come over, without explaining why on the phone. Jack begs for another chance, calling Monk his big brother. When Stottlemeyer arrives, Monk can't bring himself to turn in Jack and pretends that Jack woke him up and Monk panicked and called the captain. As Stottlemeyer leaves, he tells them that Shiv died in prison, stabbed to death.
The next day, Monk talks to Dr. Bell and admits that Jack is staying with him. Bell tries to assure him that questions about what people owe their relatives is a common issue. However, when Monk mentions Jack's interested in Paraguay, Bell notes that he works at prisons and that Paraguay is considered the "promised" land because they refuse to extradite anyone except murderers. Monk goes back to his apartment where Jack is conning Natalie out of money. Monk confronts Jack over Paraguay, since Jack wants to get cleared so he can flee to Paraguay without being extradited. Natalie grabs hr check back and Monk realizes that Jack stole a watch from Lindsey's apartment. However, Jack points out it's a man's watch and Monk notices an inscription, and realizes what happened.
Monk, Jack, and Natalie go to prison guard Reese's home, where Reese greets them while drinking coffee. Monk points out the watch is engraved "LB to DR" but Reese says there's three people with the initials DR at the prison. He says he has a wife and kids and wasn't having an affair. Monk apologizes and leaves, but explains to Natalie that Reese had a sterling silver spoon in his coffee with "GOSF on it. Reese realizes they know he killed Lindsey and opens fire. They duck for cover and Jack fires back, using the gun he stole from Monk. Monk explains that Reese and Lindsey were lovers, it went back, and Lindsey threatened to tell Reese's wife. He killed her, and then set Shiv up by providing him with an escape plan. When Jack knocked out Shiv and took the escape, Reese set him up instead. With their cover shot away, Jack volunteers to run to the car to get Natalie's cell phone and call for help. Natalie throws him the keys, he runs to the car… and drives away. Reese moves in for the kill, but Jack comes back and runs him over.
Monk and Natalie go the court house where Jack is being taken back to prison. He confessed to the DA and will get extra time for his escape, but he's been cleared of the murder charge. Monk finally acknowledges that he 's proud to consider Jack a full brother, rounding up from being a half-brother. Jack prods Monk into giving him a hug. However, as Jack is taken away, Randy notices that his handcuff keys are missing…