Lightman is called to testify in the trial of a beautiful widow accused of murdering her much older husband.
After an older man and his young wife make spirited love, she says she'll be back shortly. Next thing we see, his body is in a coroner's bag.
As the young wife, Clara, approaches a courthouse, a woman shouts inappropriate questions. Clara's attorney -- Cal's ex-wife, Zoe -- guesses who's behind them.
When Cal watches this on videotape, he detects more sadness than guilt in Clara, but he agrees to serve as an expert witness for Crosby, the prosecuting attorney who says Clara killed her husband, Victor, for his millions. Zoe interrupts their meeting and threatens to tear Cal apart on the witness stand. And Gillian accuses Cal of taking the job to get back at Zoe.
In the courtroom, Eli (who thinks Clara's guilty) and Ria (who doesn't) study the jurors. When Cal tells the judge he doesn't believe a "whole truth" exists, the judge asks if he can be honest to the best of his ability. He can do that.
On the stand, Cal dismisses Clara's alibi that finding Victor dead caused her to lose all memory of the 40 minutes after she last saw him alive. Cal argues that 90 percent of memory loss claims are false.
Zoe cross-examines Cal, noting that he once accused her boss of sleeping with her and her boss is gay. Cal pleads jealousy, explaining that he's a scientist by day, but in his personal life he's fallible. When Cal calls Clara a liar, the judge orders the bailiff to remove him.
Outside the courtroom, Cal takes advantage of a distraction that he helped create to question Clara alone. Zoe discovers this, has Cal jailed for client tampering, but she gets him released when he says Clara is innocent.
Meanwhile, Gillian is coaching witnesses: Victor's son, Damian, and his longtime friend and CFO, Leo. The latter is smooth; the former isn't, but he claims Clara had sex with him several times. When Gillian presses Damian about this, his story lacks specifics -- and he turns smooth, effortlessly pouring coffee while recounting the tale.
When Cal shows Clara photos of Damian and her old friend, Tanya Wilson, she shows contempt and anger, respectively. Clara denies having sex with Damian. Gillian believes her and brings Damian back for further questioning. When Damian sees Cal and Clara kissing, he gets angry and calls her a slut. Clara slaps Damian. Cal believes Damian's sexual relationship with Clara is pure fantasy.
Crosby accuses Cal of switching sides. Zoe tells Crosby that Damian is lying and if he testifies, he'll be indicted for perjury. Cal tells Crosby he gave his opinion, prepped the witnesses, and read the jury, so his job is done. Crosby is angry, and Cal thinks he's hiding something.
Leo testifies that he found something suspicious in the estate yesterday. Zoe argues this should've been disclosed in the deposition. The judge overrules Zoe. Cal calls Leo and Crosby liars and gets kicked out of court again. Leo says Clara had been siphoning off $90,000 a month for the last 18 months.
Cal accosts Tanya -- who's been in court every day -- outside the courtroom, asking why Leo's testimony scared her. Cal says Tanya's presence isn't motivated by concern for Clara, but to ensure Clara's silence, so what's she hiding? Photos of Tanya, Clara, and Victor having a three-way, says Tanya, explaining that she introduced Clara to Victor -- "Her life was supposed to be mine" -- and they wouldn't miss the money. But Cal's been recording this conversation and demands Tanya turn over the photos or face blackmail charges.
Clara explains that the three-way was a birthday present to Victor, done to fulfill a fantasy. And her false memory loss was to conceal that she was paying off Tanya during that time. Victor didn't know about this, and Clara didn't want the tape to surface because it would've damaged Victor's upstanding reputation.
Cal asks Zoe to call him back to the witness stand, where he reveals secrets the various jurors are trying to hide, then he accuses Leo of being the killer, which Leo denies. Cal replies Leo didn't murder Victor, but the regret on Leo's face indicates he killed him.
Zoe shows Tanya's photos to the judge and Crosby -- asking they be kept out of open court to preserve Victor's reputation -- then puts Leo back on the stand. Leo admits knowing about the photos. Just like Clara, he was protecting Victor's rep. So why finger Clara for murder?
Leo claims Victor's doctors had given him only a month to live, but as a devout Catholic, Victor couldn't take his own life, so he asked Leo to do it -- and Victor left a videotape explaining this. Zoe asks that Clara be allowed to view the tape, which confirms Leo's story.
Back at the office, Zoe explains that Leo pled guilty to obstruction of justice and manslaughter. Clara is grateful then asks Cal about his relationship with Gillian. "She's my Leo," he replies. And Zoe? Cal says he never stopped loving her. Clara explains that she'll be taking over Victor's business and wants someone she can trust to advise her. Cal agrees to do so.
Over a celebratory restaurant dinner, Zoe asks Cal why he took the case. When Cal answers he wanted her to get the respect she deserves for winning, Zoe says, "That's sweet and paternalistic. And patronizing," adding that she's still waiting for Cal to get what he deserves.
Then Zoe says Emily is spending the night with a friend -- and she and Cal exit together.