Sherlock is called onto a crime scene were a man has been murdered and robbed. There he meets Marcus Bell, Captain Gregson's new partner. After inspecting the scene, Sherlock asks Marcus if he considers it a robbery-homicide, and when Marcus says yes Sherlock disagrees stating that the crimes were separate. Sherlock sniffs a chair and deduces that the homicide was commited by someone sitting and wearing perfume, probably female since it's a floral scent. The robbery was committed by a strong man based off scratchmarks on the floor made from moving a large piece of furniture, which Watson backs up by pointing at pictures of the same apartment.
Since the apartment has no elevator, Sherlock determines that the robbery culprit can't be far. He breaks down the door on the neighbor's apartment, and sure enough the wardrobe is there. The neighbor is arrested, but Sherlock does not believe that he is the killer. The neighbor claims that he passed by a woman wearing the perfume, but Bell believes that he overheard Sherlock's deduction and made it up.
Tropes:
- Always Identical Twins: Averted when the witness drawing matches a woman who just happens to be in a coma. After finding out the woman has a twin, Holmes seizes on the twin sister as the killer until they go to meet her and find out the two women are fraternal, not identical twins.
- Chekhov's Gunman: The doctor of the woman in a coma was keeping her in a drug induced coma as an alibi for her murders.
- Convenient Coma: Invoked In-Universe, where the killer was slipping in and out of a medically-induced coma with the help of her doctor boyfriend, in order to have the perfect alibi.
- Evil Twin: Subverted. There is an evil twin, but she's fraternal, not identical, so there's no impersonation of the good twin. Some aspects of this trope are played with, namely framing/trying to kill the good twin.
- Fake Alibi: The murderer has her accomplice place her in a medically induced coma so everyone will believe she's completely immobile and helpless. Late at night when nobody is watching, the accomplice takes her out of the coma so she can murder her targets and puts her back into the coma by the next morning.
- Funny Background Event: While Joan is talking to her ex-boyfriend on the phone, Sherlock places his violin in a metal garbage can, and sets it on fire with a giant whoomp.
- Inheritance Murder: Variation. The killer was targeting her siblings so she would be the sole heir of their wealthy father's estate.
- Ironic Echo: Holmes attempts to test whether a coma patient is really asleep by jabbing a needle into her thigh, proclaiming that there are "lots of nerve endings there." Later, Watson threatens that if he falls asleep during his NA group session, she'll do the same to him.
- Men Don't Cry: Averted with Sherlock when he nearly cries by the end of the episode.
- Mirror Character: Joan sees similarities between her and Sherlock's emotions regarding themselves and their pasts.
- Mythology Gag:
- Sherlock tells Joan that his brain is "like an attic, with a finite amount of space" that he must save only for the necessary, which is an exact copy of the analogy Holmes gave to Watson in the original stories- but with more tossing around complete strangers' glasses of water.
- Watson finds an old violin that Holmes owned and tries to get him back into it, saying that playing an instrument will help him stay sober. The original Sherlock Holmes was notorious for playing the violin while thinking.
- The Nose Knows: Sherlock works out that the killer is a woman after noticing the scent of a women's brand of deodorant on a chair in the first victim's apartment.
- Polar Opposite Twins: As Sherlock notes, Rebecca Ellison is a kind-hearted woman who is happy to share her inheritence with her half-siblings. Her twin sister Yvette is a selfish, manipulative murderer.
- Rich Bitch: Yvette Ellison, who not only murdered her newly discovered half-siblings, but also faked a coma and plotted to kill her own twin sister, solely because she did not want to share the family inheritance.
- We Will Meet Again: Sherlock warns a suspect that "You haven't seen the last of me!" as part of a setup.
- You Need to Get Laid: Sherlock advises Joan that she should take up her date's invitation to a second meeting because it would help her mood.
