This week's Miss Fisher's Murder Mysteries cold open gets straight to the point, as the body of a young girl washes up on the beach in the dark. She's one of the disadvantaged girls Phryne is teaching social graces to, along with Jane and Marie (Eva Lazzaro), in preparation for the Flower Show. Considering Marie is more interested in what she can palm off the breakfast table, lessons are less than successful. Rose (Taylor Ferguson), another student, interrupts, late for lessons and without the fourth student, Kitty, who never showed where they meet at the bathing boxes. Determined to round up all her charges, Fisher declares they'll all go to the beach.
Robinson: A liar, an arsonist, and a flower maiden. I'm beginning to appreciate Miss Fisher's challenge.
It isn't long before they find Kitty's body, and Robinson is called in. Jane is shaken, insisting Kitty was a strong swimmer. Marie tells Robinson it's suicide over a boy, but Jane and Rose call that nonsense, though Jane admits Kitty collapsed a few days ago. The only address on file for her is the same as Rose's. She says Kitty used to be employed by her grandfather as a laundrymaid but hadn't worked for them in some time. She stubbornly refuses to say why Kitty called her to meet at the beach before Miss Fisher's class.
Unlike the others, Rose is not a welfare case, but a teen delinquent, with pyromaniac and self-harming tendencies. Robinson and Collins run her home and ask her grandfather, Franklin Weston (Terry Norris), for details on Kitty's employment. He says he let her go six months ago. As he fumbles for the reference letter he wrote for her, Collins notes the telephone cord's frayed to pieces, putting the lie to Rose's claim Kitty rang her to meet at the beach. It turns out the phone's been out since a suspicious house fire ten months ago. Franklin never paid to have it restored, and it's obvious the family is on hard times.
Rose admits she and Kitty had a standing date to party, but Kitty insisted she was done with that scene. They fought, and Kitty smacked her head. Rose tried to get help, but when she returned, Kitty was gone. Rose waited all night, but she never returned. Collins turns up Kitty's purse, with a school pin and bits of a beer coaster. When reassembled (by Dot), it has a bunch of names on the back. Phryne and Dot put two and two together: the fainting, the weight gain. These were potential baby names.
Back at the dance hall, the mayor, Lionel Phillips (Andrew S. Gilbert), is horrified to learn of the tragedy. So is his nephew, Derek (Ben Schumann), who'd been helping as a dance partner. But the mayor won't cancel the Queen of the Flowers event, even though Phryne points out teaching girls social graces isn't much use if they can't walk the streets safely. Frustrated, her next lesson, right there in the dance hall, is self-defense. That might help Jane's state of mind; she's been rattled since seeing a woman waiting outside the Fisher house. But when the woman, Anna Ross (Danielle Cormack), comes to call, she turns out to be Jane's long-missing mother.
Derek arrives at the dance hall with beer from the same brewery as the coaster and his school jacket sports the same badge as the pin in Kitty's purse. Rose murmurs Derek was too sweet on Kitty to hurt her as he's taken for questioning, but Marie snaps Kitty wanted to trap Derek since she was pregnant. Derek tells Robinson he gave the badge to Marie, not Kitty. He insists he also didn't go to the bathing sheds, though she'd wanted him to. Mayor Phillips shows up and confirms his nephew's alibi; they'd been home together. Just then, Rose rushes into the station, demanding to know if Kitty was pregnant. But one look at the Mayor and Derek and she goes white, practically stumbles in her hurry to get out again.
The key in Kitty's purse winds up being to a bathing shed where she'd been living. Once owned by the Westons, it was repossessed due to Franklin's gambling addiction, which also cost him his job and council position. There's empty beer bottles (same brewery), and a man's razor. But Derek's barely old enough to Another round with Robinson, this time without his uncle, reveals he loved Kitty, he was just overwhelmed by her desperate need to get married, unaware she was pregnant. (It wasn't his, she was three months along; they'd only been together six weeks.) Marie agreed to cover for him, saying the pin was hers. When he told his uncle, Phillips also lied to cover for nephew. They'd not been together.
In mourning, Rose goes to Kitty's shed. She's playing with her lighter when someone else stops by as well. The next morning both she and Jane are missing. Jane snuck out to see her mother, bringing supplies and money stolen from the housekeeping jar. She also brought the adoption papers to sign so that Fisher can have full custody. But Jane isn't safe there, as we discover Anna is mentally ill and begins to have an episode when her apple cake turns out wrong. She nearly commits suicide when the landlord (Kevin Hopkins) starts slamming on the locked door. Robinson and Phryne arrive just in time to save Jane's mother. Fisher promises Jane they will keep Anna from an asylum.
Fisher and Robinson find Rose in the bathing shed after a suicide note shows up at Franklin's house. She's swallowed a bottle of pills, but keeps saying, "He made me do it." He turns out to be Mayor Phillips. Rose admits Phillips tried to seduce her, her grandfather selling her to curry favor and get reinstated, but when Kitty showed up, Phillips decided she was a better bargain. Phillips set Kitty up in the shed and was the father of her baby. The fight on the beach hadn't been about partying. Kitty wanted to go public and expose the mayor. Rose regrets her refusal.
When Phillips is arrested, he sneers at Fisher. No one will take the word of a troubled young girl over him, but Rose stands firm. Fisher's school may not have taught anyone social graces, but it let one young woman learn to demand justice.