The naked corpse of a woman is found in an office building. Evidence suggests that the deceased is Lucy Sullivan, who was visiting New York from Indiana. But Lucy is alive, and identifies the victim as her sister Joanne. The detectives learn that Joanne and her husband Billy Dunbar were running a scam in Atlantic City, and local mobsters took out a hit on them. They fled to New York, but now appear to have been hunted down - Billy Dunbar is missing, and Joanne was murdered in the office he'd been renting.

A search of Dunbar's apartment uncovers the gun that killed Joanne, and the building supervisor testifies that Lucy was there with him. Fingerprints on the gun are a match to Lucy's, and she is charged with murder. The People's case is that Lucy had an affair with Dunbar and killed Joanne in a fight about it. Soon, Dunbar is found dead in an evident mob execution.

The judge, Marks, has an unusually hostile attitude towards the [=DA=]s. He repeatedly behaves inappropriately toward Ross - even in court! Lucy refutes the building supervisor's testimony by producing evidence that she was in a ticket office booking a bus tour. But to do that, she'd have had to show ID. This leads [=McCoy=] to discover "Lucy" is Joanne. She wanted to save her own skin from the people trying to kill her, so she murdered Lucy and assumed her identity.

Marks grants the defence's request for a mistrial, and [=McCoy=] re-indicts. This time, Marks is even more aggressive. He actively hampers the prosecution's case and even has [=McCoy=] locked up for contempt. Schiff successfully requests to get Marks removed from the case on account of his obvious bias. With a new judge in place, Joanne's lawyer asks for a plea. When [=McCoy=] refuses, Joanne says that Lucy "didn't have a life"; she lived in Indiana and worked in a dead-end job. Joanne is convicted, but Schiff regrets what's happened to Marks, who had thus far always been genuinely concerned about justice.

!!Tropes in this episode:
* AccentRelapse: Joanne tries to adopt a Midwestern accent to pose as Lucy, which she drops when her real identity is discovered.
* BlackComedy: The judge has a pronounced bias against the [=DAs=] and at one point he even finds [=McCoy=] in contempt, leading to the scene where Schiff finds him in a holding cell with three other detainees.
* BlatantLies: Joanne tries to claim that Dunbar didn't come home one night, and she knew he'd been murdered; so she wasn't thinking straight when she killed Lucy. This is such a ridiculous lie that [=McCoy=] doesn't even bother to acknowledge it - he already knows Dunbar was at home with Joanne on the morning of the day Lucy died.
* CountryMouse: As "Lucy", Joanne pretends to be unfamiliar with New York and unused to city life - although the real Lucy was from Terre Haute, a small to medium-sized city.
* DoubleMeaningTitle: Refers to both Joanne's identity theft, and how [=McCoy=] found out about it (looking into the ID she would have had to show to book the bus tour.)
* {{Hypocrite}}: Judge Marks claims to have written sexual harassment protocols, yet seems determined to be utterly oblivious to the fact that that's what he was he was doing to Jamie.
* {{Jerkass}}: Judge Marks, who repeatedly and inexplicably acts hostile to the prosecutors and sexually harasses Jamie.
* KillAndReplace: Joanne [[SiblingMurder murdered her sister]] in order to take her identity.
* LeftHanging: It's never explained why Lucy's corpse was found naked, although Joanne may have forced her to strip at gunpoint in order to steal her clothes.
* PlayingSick: Played with. Marks doesn't voluntarily do this, but it's the excuse given to the jury as to why he's been removed from the trial at a late stage of proceedings.
* SiblingMurder: Joanne murdered her sister.