Isaac and the player are informed by Constable Ramirez that another prostitute has been found dead at the hands of the Scarlet Slayer, her body lying in an upstairs bedroom of the famous Moulin Rose cabaret. There, both officers see the corpse of Gladys Perrin, the barber shop assistant who had just returned to being a prostitute, with her stomach sliced open and a dove feather resting on her torso.
Tropes:
- Agonizing Stomach Wound: Defied by the Scarlet Slayer who, according to Dick, made sure Gladys was sedated with chloroform before slicing her open. Judging by how Fiona reveals during her arrest that she was doing a "Mercy Kill" to the prostitutes she killed, it makes sense she wouldn't wanted them to suffer.
- Ax-Crazy: Isaac calls Fiona out of her mind when she reveals her reasons for becoming the Scarlet Slayer, namely taking prostitutes out of their misery so they wouldn't suffer at the hands of abusive clients and calling them "falling doves" she returned their wings to.
- Bad Boss: Seamus says Fiona is even scarier than the law and that's why she helped her escape from her cuffs when she came to him. And considering how she murdered all of those prostitutes working under her and her brother, his claims aren't that far from the truth.
- Bait-and-Switch: Diego says this when you ask him for help regarding Charlie being scammed by a Con Man.Diego: Just because I'm a con artist you think I might know every crook in Concordia?Well, you're perfectly right!
- Big Damn Heroes: Diego comes in to save Charlie's money during the Additional Investigation after he gets scammed and left penniless by a Con Man, recovering his money without asking for something in return.
- Call-Back: Vinnie Costa, Marla de Paradis, and Fiona Flanagan reappear as suspects. Finley Flanagan and Seamus O'Neill also momentarily appear in minor roles.
- Call-Forward: The Kingdom of Mazunda is mentioned by Charlie during the Additional Investigation.
- Cliffhanger: The case ends with the Flying Squad rushing to an opium den where Fiona is hiding after having escaped from the police car taking her to prison, intending to capture her and end with the Scarlet Slayer nightmare once and for all.
- The Con: Charlie falls victim of one during the Additional Investigation after being scammed by a Con Man telling him that the prince of Mazunda had been kidnapped and they needed Charlie's money to rescue him, promising to pay him once the prince was rescued. Fortunately, Diego manages to recover his funds.
- Cooperation Gambit: Seamus lands himself just a few days in jail due to cooperating with Fiona's escape since he also told the police a lead about her whereabouts.
- Desperately Looking for a Purpose in Life: Marla claims that, ever since her fiance died, she's been looking for a way to escape her life in Sinner's End, not wanting to spend the rest of her days as a cabaret dancer among prostitutes and death.
- Door Slam of Rage: Finley does this after he warns you that you better catch the Scarlet Slayer before sunrise, since the presence of cops in her cabarets is scaring off his girls.
- Eccentric Artist: Henri Leclerc is an artist who likes drawing the prostitutes of Sinner's End (often in pretty nightmarish ways) and speaks in full Purple Prose.
- Fate Worse than Death: Fiona sees being a prostitute as this, claiming that she became the Scarlet Slayer to put girls out of their misery due to the abuse they suffer at the hands of other clients.
- Great Escape: Fiona somehow manages to escape from the police car transporting her to the courtroom and also manipulates Seamus into sawing off her handcuffs, allowing her to escape after her arrest.
- Guest-Star Party Member: Once again, Diego joins you during both the main and the Additional Investigation with some analyses without being an official part of the team.
- Gutted Like a Fish: How Gladys was killed, courtesy of the Scarlet Slayer's M.O.
- Hidden Weapons: Marla becomes a suspect after you find her blade-concealing fan in the crime scene, which she carries around in case the Scarlet Slayer decides to target her.
- In the Hood: The Scarlet Slayer wears a (naturally) scarlet-colored one.
- Mad Doctor: Irving Blackmoor, a misogynistic, Slut-Shaming doctor who likes to perform surgery on female patients without anesthesia, appears in this case as a suspect. No wonder why Isaac puts him as his number one suspect on who the Scarlet Slayer could be.
- Major Injury Underreaction: Dick during the autopsy report, courtesy of his Professor Guinea Pig status.Isaac: Richard, you have a... a scalpel sticking out of your neck!Dick: Oh, yes! I was testing a new formula for anesthesia, and I completely forgot the blade was there.
- Mercy Kill: Fiona firmly believes that she's doing the prostitutes she kills a favor by saving them from a life of being abused and degraded, claiming that they're fallen doves and she just returned their wings to them.
- My God, What Have I Done?: Seamus has this reaction when you inform him that Fiona, who he helped escape from her cuffs, was the Scarlet Slayer, as he believed she was being taken to prison for her alcohol business.
- Nightmare Fetishist: Dr. Irving Blackmoor tells you that, while operating patients without anesthesia is immoral, he also considers people's screams to be "extraordinary".
- "Not So Different" Remark: Fiona attempts to do this while you interrogate her about the murder.Fiona: The girl's body is barely cool and you are already sniffing into her finances? What principles?
- Oh, Crap!: Judge Lawson justifiably has this reason when Constable Ramirez informs him that Fiona has escaped on her way to prison.
- Opium Den: The Flying Squad goes to one at the end of the case to intercept Fiona, who Rose has found is hiding in there.
- Pun: One regarding a bottle you find for Vinnie Costa.Isaac: The bottle's label reads, "To our best COSTA-mer! Compliments of the Moulin Rose." Is this a pun?
- Race Against the Clock: Finley puts you a time limit until sunrise to solve the crime or else he will step in and make you leave, although Isaac doesn't believe his threats.
- Red Herring: Everything about Dr. Blackmoor practically screams that he is the Scarlet Slayer, when in reality it's Fiona.
- Shout-Out:
- The case's title comes from a lyric of the song Cabaret, originating from the musical of the same name, "Life is a cabaret".
- Irving Blackmoor resembles Dario Argento.
- Henri Leclerc is a parody of Henri de Toulouse-Lautrec.
- Phantom of the Cabaret is a parody of The Phantom of the Opera, with Viola singing a lyric close to one from the titular song.
Viola: The phantom of the cabaret is here! Inside your soul!- Moulin Rose is a parody of Moulin Rouge!.
- Honoré de Balzac is quoted.
- Sibling Rivalry: During both Fiona's interrogation and arrest, Isaac asks if the reason why she's been killing prostitutes is to spite her brother, as the alcohol prohibition has made her business less effective than Finley's prostitution ring and therefore she might want to level the playing field. As it turns out, Fiona's reason for killing her brother's prostitutes is a much different one.
- Slut-Shaming: This is why Dr. Blackmoor performs surgeries on prostitutes without anesthesia, as he's a Straw Misogynist who believes all women are born sinful and deserve to be punished. Isaac is understandably horrified by this.
- Stalker with a Crush: Vinnie was in love with Gladys and even sent her a stalking note claiming that he had an eye on her.
- Tragic Keepsake: Marla keeps a page of Dr. Wilson's anatomy book with her as a keepsake since his death in Case 19.
- Two Aliases, One Character: As of this case, Fiona Flanagan isn't only the Irish gang leader known as "The Viper", but also the bloodthirsty Serial Killer nicknamed the "Scarlet Slayer".
- Unwitting Pawn: Seamus unknowingly helped the Scarlet Slayer escape from prison by sawing off Fiona's handcuffs, believing she was being arrested for selling alcohol instead of the whole serial killer ordeal.
- Yank the Dog's Chain: Poor Gladys got killed by the Scarlet Slayer just when she had started to collect enough money for her sick mother's medications.
