The third episode of Miss Fisher's Murder Mysteries' starts in an alley, where a gunman watches a seedy-looking gentleman caller convince a flower seller to slip off for a roll in the hay. Meanwhile, Phryne is having a night out at The Green Mill jazz hall, complete with a live brass band and singer Nerine Rogers (Deni Hines). Phryne's dressed to dance, but she's really attempting to buy an airplane called a "Tiger Moth." Her date, Charlie Freeman (Toby Schmitz), is selling it cheap. He never learned to fly as his older brother, Vic, who should have taught him, never came back from the war.
When Charlie gets pulled away by a man in glasses and tossed about by the seedy man from earlier, his need for cash starts to look alarming. But before Phryne can investigate, she's off to dance with the band leader, Tintagel Stone (Simon Lyndon). That's interrupted when the seedy man drops dead in the middle of the dance floor, stabbed. By the time Robinson and Collins show up, Fisher's learned the victim is Leonard Stevens, and his flower girl date is Pansy Shore (Lauren Clair). The murder weapon is missing, but Stevens had rolls of cash on hand.
While waiting to be searched and questioned, Nerine makes fun of Pansy's claim Stevens was going to marry her. When Phryne digs a bit deeper, Nerine admits she didn't know Stevens well, but he'd been hanging around the club since it first opened, and she knows a creep when she sees one. She and her husband, the cornet player Ben (Arthur Angel), recall seeing very little; she was serving drinks, he was on stage. On the other hand, Jack notes Miss Fisher's original date, Charlie, bolted and left the scene as soon as Stevens died.
The next morning, Fisher is talking with Dot about asking Constable Collins to the Policeman's Dance if he can't get up the nerve, when a call comes in from Charlie's mother, Adele (Wendy Hughes). Charles has disappeared, and she's frantic they'll hang him, taking away her only remaining son. She points Fisher in the direction of one of Charlie's ne'er-do-well friends, Bobby Sullivan (Adrian Auld), in hopes he might know something. Bert and Cec head out to find Sullivan at his favorite dart-playing haunt, while Miss Fisher pops round to see the body, to the horror of Dr. Johnson (John Arnold), who is examining it.
The doctor opines the knife wound was thin, like a rapier, to which Miss Fisher pulls out her hat pin and models how it could be the perfect match. Meanwhile, Bert and Cec bring round Sullivan, who turns out to be the mysterious man in the glasses who left before Stevens' murder. He lies his way out of her house, but when Bert, Cec, and Fisher tail him down, he's climbing a drainpipe into Leonard Stevens' apartment in a desperate rush. Fisher climbs up after him, and searches the study, finding a wedding invite for Leonard and Patsy in the wastebasket. Luckily, Robinson and Collins have just arrived too, in time to see her go in the window.
Miss Fisher happily introduces Sullivan to them as "Charles' good friend" who broke in ahead of her. The papers Sullivan was after turn out to be photos of him and Charlie in bed, taken by Stevens. They'd been blackmailed for months, hence Charles' need for money. Now they'll be tried for sodomy as well as murder. But Charles wasn't the only one contributing to Stevens' bank account. So was his mother, every month for the last two years. Fisher goes off to find out the truth, and sends Dot, still without an invite from Collins to the dance, to the church on the wedding invite to see if banns were posted.
Steven, it turns out, used to work for the Freeman family as "an accountant" but was fired. But Adele knew nothing of her son's taste in men, so the payments were for something else she's not telling. Meanwhile, Dot learns the wedding was canceled the day after banns were posted, making Pansy a jilted bride. When Fisher hunts down Pansy, she admits Len cheated on her regularly, recently with a woman with strong perfume, which Fisher recognizes right away as the scent Nerine wears. But the second round of questioning shows Nerine hates Stevens, so Fisher guesses there must have been more blackmail involved.
Fisher takes Stone home hoping to seduce him into answering some questions. He bolts, but not before she gets her hands on a photo with the mysterious gunman from the top of the episode, who, to her shock, is Vic Freeman (Rohan Nichol). He survived the war, living in PTSD-driven solitude, which is what Adele was paying to hush up. Dot hands the photo to the police and asks Collins to the dance while she's at it. Fisher and Charlie take the plane to see Vic, while Collins turns up why Narine was being blackmailed. She's still married to her first abusive husband back in Virginia. Ben flips when he finds out, leaving her to confess to the murder. But her confession shows she doesn't know how it was done.
The good news means the killer isn't Charlie or Vic. But Narine knows who did it, and she's protecting him. It's then Fisher puts together the clues: Narine's sudden horror looking at the stage, Ben's horn, and the mute, which has a perfect hole in the center for a dart or a pin-sized weapon to be blown through. Hearing she confessed to protect him, Ben breaks down and tells the truth that he murdered Stevens out of jealousy, thinking Narine was having an affair, not knowing it was blackmail all the time.
Satisfied the case is closed, Robinson quietly turns over the photo plates of Sullivan and Freeman to Fisher. He can't make them disappear, but she can. She happily leaves Robinson in his office, as Collins and Dot head to the dance.