At a casino, John is playing blackjack while Karen looks on. John quickly starts winning and rattling off probabilities to help his fellow players win. The players are thrilled but John goes with her instincts and takes a hit, while John loses playing the probabilities.
At an art museum, two guards hear an alarm and head to the west gallery, where they meet other guards and go in to find that that a valuable diamond ring, the Bishop's Ring is gone and a guard, Cheryl Evans, is dead, wearing a pair of handcuffs and shot with her own gun. Frank investigates the disappearance of the ring Bishop's Ring. The museum director claims the theft is impossible and the tape shows Evans falling from behind a statue but there's no sign of a shooter on any other camera. The camera covering the ring has been moved. Faced with an impossible crime, Frank calls John Doe.
John checks out the room where the shooting occurred and determines the room has high security but the alarms have been moved out of alignment. John then demonstrates how the thief managed to get in by showing the gap in the camera coverage by hiding in a sculpture. John doesn't know how the thief escaped, and the dead woman's son Lewis shows up and Frank has to break the news to him. Later John is working out the angles at his apartment while Karen cooks and plays loud music but perks up when she hears about the museum. She quickly takes off, and is nervous when Frank arrives.
Frank and John go over the list of suspects and John notices the name of an underground photographer, Max Clark, who had a piece rejected by the museum. They head for the police department where Stella comes up with a camera showing a tour guide in a nearby stairwell – Karen, letting someone in through a fire door.
Frank interrogates Karen while John believes she's innocent. Avery reveals that Karen is a foster kid who has been in trouble in the past. Karen has nothing to say and Frank leaves her for the DA. In court the DA hammers her about her presence at the crime scene, and her public defender her has her talk about how she brought in her boyfriend Colin and they set off the alarm, but they had nothing to do with the robbery. John arrives to take over from the public defender and quickly recites off enough citations and titles to convince the judge to let him represent Karen despite the fact he's now a lawyer. Karen agrees to let him take over and he shows that she was at a photocopier a minute before the alarm went off, and given her shoe size there's no way she could have got to the stairwell in the time indicated.
That night John visits Karen at home and meets Colin. Karen tries to get him out but John overhears a message from…Max Clark, who says he'll be leaving town and wants to meet with her. John takes his suspicion to Frank and they confront the photographer, while Frank discovers Cheryl Evans' body has never been checked in. Frank and John interrupt a party and it's clear Max is in to underground-style body-art photos. When Max proves reluctant to talk, Frank has him hauled away while John spots Karen as a model in one of the photos.
Avery interrogates Max and John and Frank figure he's lying. Max claims to have an alibi and the police verify it and have to cut it loose. John returns to find that Karen is moving out and is upset that he snooped around her apartment. John doesn't believe her claims that Max is innocent and she points out she's going on instinct, not logic. She leaves, as John wonders why he feels nothing by looking at art.
John goes to police HQ and Frank is out, but he meets up with Nance who insists they never received Evans' body in the first place. John remembers seeing a coroner's assistant take the body away based on the photo ID, which he goes to Max's loft to connect it to the photographer. He finds computer files that show Max created a fake ID. Frank puts an APB out on Max and John notices that the building has a basement large enough to store a fake coroner's van. Checking it out, they find the fake van and Evans' gutted corpse. John concludes that's how Max got the diamond out, by hiding it in her body.
At the autopsy, Frank believes Evans was forced to swallow the diamond at gunpoint but Nance and John notice that Evans had terminal stomach cancer. From that John figures that Evans shot herself – she was the inside man and slowly moved the camera out of alignment over several days. Stella analyzes the security cameras and they figure she put on the handcuffs and faked being shot, and later Clark came in to take her away. While they continue the search for Max, John goes to Karen's apartment and she lets him in and apologizes. Going over her photos with Max, John concludes he was above mere murder. He and Frank go to visit Evans' son Lewis and find Max there. Max reveals that since Evans' cancer was a pre-existing condition, she wasn't covered by museum insurance and Max, her friend, decided to help her so her bills were covered.
Frank insists a crime has been committed and John wonders if he could have been so loyal to someone he loves, and Frank points out he's protected Karen. Later Karen and John visit an art museum and John asks her to stay around, and she agreed, admitting they're family. And John finally makes a connection with a painting, as it marks their moment together.