Hotel cleaning staff find the body of Nathalie Dreisner, a star violinist with the Manhattan Symphony Orchestra. Green and Briscoe find out that Nathalie was having an affair with Carl Reger, the orchestra's conductor. Reger was very controlling over Nathalie's career and his wife, who's also with the orchestra, was threatening her. On the night Nathalie died, she'd planned to give Reger her resignation. The detectives gather enough evidence to arrest him for murder. But the case goes to Judge William Wright, who has a long history of enmity with McCoy. He instantly agrees to exclude key evidence on a technicality. The prosecutors are angry that he's obviously planned this so it won't look like bias.
Wright denies Lewin's request that he withdraw from the case. He threatens that if she reports him, he will make sure her DAs don't stand a chance in his courtroom ever again. Lewin warns him not to step out of line. Meanwhile Reger, who's a respected figure in the community, has the media on his side. His wife won't budge on the alibi she gave him. In court, Wright surprisingly allows McCoy to make a point about the implausibility of Reger's story, against the wishes of the defence. Lewin suggests the prosecutors look into the Regers' finances. They make $2m a year but now say they're struggling to pay their legal expenses.
Carmichael and McCoy confront Mrs. Reger with the knowledge that Reger has been hiding assets from her in a Swiss bank, planning to divorce her so he could marry Nathalie. Mrs. Reger agrees to testify, and when McCoy says he'll appeal if he has to, Wright allows it. But on the stand, Mrs. Reger now says she killed Nathalie. Wright calls a recess, and Mrs. Reger says she had no choice after her husband talked Nathalie out of leaving. She agrees to plead guilty to murder. Carmichael and McCoy aren't sure if she is telling the truth, or still covering for Reger.
This episode contains examples of:
- The Ace: Dreisner made second string in the orchestra after just three years out of Juilliard, ahead of others who'd been with the orchestra for more than twenty years. Even if she hadn't had an affair with Reger, her talent was prodigious enough for her to make it on her own merits.
- Deadpan Snarker: Lewin gets in a few such moments against Wright.
- Double-Meaning Title: Refers to the resentment of Nathalie within the orchestra; the Regers' marital problems; and the fight between Wright and the DA's office.
- Murder the Hypotenuse: Mrs. Reger claims this as her motive.
- Spousal Privilege: As a witness, Mrs. Reger isn't allowed to repeat anything her husband may have said that would fall within the remit of this.
- Swiss Bank Account: Mrs. Reger is floored when she is shown evidence that her husband has been transferring money from their account to accounts in Swiss banks in his name only.
