This week's Miss Fisher's Murder Mysteries cold open begins at the 3JH Radio Station as a woman gets murdered in an office. Convenient that, since Fisher just got a wireless radio with channel 3JH. But there's something wrong with today's broadcast of The Polkinghorns, as the actress who plays Guinevere is late, and Collins is outside the door.
Actors Jimmy and Hazel Creswick (Marco Chiappi and Pip Edwards) attempt to cover. However, the broadcast is interrupted by the foley man Clarence Ball (Rhys Muldoon) declaring the actress, Louisa Singleton, is dead. Fisher and Dot turn off the radio and head out, ready to investigate.
Jack: And now for some modern music from ...Beethoven.
Dot knew Louisa from school, giving Fisher an extra excuse when introducing herself to Jimmy, who is also the station manager. But where is Jack? Collins whispers he's gone undercover. Inside, Fisher realizes Louisa was killed in the office and notes the station's pet goldfish is dead. Jimmy and Hazel insist Louisa had no enemies, though she did break it off with a fiance in Perth to take this job. Hazel says there were threats made against the station, but Jimmy admits that's been happening a lot in the radio world. They'd personally been on a high, with Hazel winning Best Female Talent at the Australian Radio Performance Awards. They also just hired Archibald Jones to do the hourly news.
But when Fisher hears "Jones," she perks up, knowing Jack's voice anywhere. Jimmy warns her to look out for Jones, who he finds suspicious. Jack is glad to see Fisher since he's currently stuck pretending to be a radio presenter. Four stations have had incidents shutting them down. He suspects Ball, who left 3XL days before it burnt to the ground. As Ball's sporting bets show airs, Bert, Cec, and Bulter are listening intently. The local pub's been making a fortune, even though the tips sound like the standard favorites.
Ball left the station after Louisa's time of death, but claims to have seen nothing, and insinuates Hazel hated Louisa. But Hazel seems genuinely lost without her, and Fisher offers up Dot to help. Dot discovers the story ideas Hazel claimed were Louisa's, and a one-way ticket home to Perth. Jimmy is shocked to see "Hazel's" script ideas in Lousia's idea book, and also insists Lousia wasn't going anywhere. He does admit he was late to the awards ceremony, and Hazel arrived after him, meaning neither of them has an alibi for the time of death. The newspaper salesman, Dodger (Travis Cotton), who was sweet on Louisa, also came around a lot. He's got a betting racket going on with Ball, and Fisher finds an empty box of his cigarettes near the body.
Fisher offers herself up to be the temporary on-air talent to see how Hazel takes to having competition. Hazel doesn't appreciate it at all, threatening Fisher and seemingly drugged, until Jimmy calms her down. As Dot brings in a new goldfish, Fisher catches Dodger dropping off "racing tips" and has Cec and Bert look them up. To their shock, Dodger's tip is good, though Ball's coverage barely mentions the winners, reciting dates instead. Still, it's enough for Collins to drag Dodger in, whose real name is Johnny Lockhart. He's the nephew of a notorious horse racer, and guilty of gambling. But Ball has plausible deniability, it's not on him if people bet on the coded tips. But with newspaper bits in Lousia stomach, one labeled Page 5, could she have threatened their racket?
In Louisa's purse, there's a specially-altered fork, which convinces Jack and Phryne to take a late-night visit to the radio station. The fork opens a hidden panel, inside there's a newspaper missing Page 5. But they also catch someone attempting to burn down the building. Fisher loses the suspect, but the cigarette pack he dropped is unmistakably Dodger's. His fingerprints confirm Dodger's the serial-arsonist; radio is killing his newspaper business. But there's no arrest. Instead, Cec and Bert find him dead the next morning.
There's an earring, which Phryne recognizes as Hazel's. Jack blows his cover to bring her in, but Hazel insists she'd lost it. Also, the new goldfish Dot brought in died, and Fisher asks for the water to be tested. Jack reports the fish have been poisoned by Thalliumr, which in low doses it causes hair loss. That explains Hazel keeling over during The Polkinghorns broadcast with her hair is falling out. When she shows up at Fisher's house to ask Phryne to fill in, Fisher tells her to stay. But Hazel insists she can't be sick. She's due in Perth next week to start a job for the National Broadcast Service, which Louisa bought the ticket for in secret since Jimmy would explode if he knew she was leaving.
Dot notes the archival copy of Page 5 has a death notice from five years back, for Perth-based radio talent "Guinevere Redpath," who performed "Twilight Melodies." "Guinevere" was the name Louisa gave her character. Collins looks up the details and discovers Guinevere's death was no accident, but never solved because the husband, Harry, disappeared. When Phryne heads to the station, she finds the record of "Twilight Melodies" in Louisa's things, and has Bell put it on. "Harry's" voice introduction is none other than Jimmy, Guinevere's missing husband.
Jimmy knocks out Ball in the hall and confronts Fisher in the studio, demanding Hazel's whereabouts. Phryne flips the switch from music to the mic, confronting Jimmy live on air, as Hazel and Dot listen. As Hazel sobs in horror and Jack rushes to the station, Jimmy confesses to killing Louisa for recognizing him and then killing Dodger because he witnessed her death. Jack arrives just as Fisher saves herself and knocks Jimmy out.
With Dot helping Collins directly this week, he notes they can get married soon, and she'll be able to quit her job. Dot is horrified at leaving Phryne, which is not helped by Fisher and Butler, who both say they couldn't imagine life without Dot. So Dot hands him back the ring, unwilling to quit her job to become Mirs. Hugh Collins. No Miss Fisher wedding after all? Thankfully, Collins decides he has to get on board with a modern wife like Dot if he's going to marry her. Hooray!