Sherlock is brought to a crime scene of a dead body in an alley with both eyes shot out. Sherlock deduces the man is a college professor, and by the colors of his tie, from Predue. Sherlock looks up the man and finds out he is Trent Annunzio, and visits his office. Sherlock notices that Annunzio's office is number 14, a lucky number to Chinese Gamblers when he could have chosen the larger and more well light office across the hall. He also notices gambling tiles, which he had individually despite them coming in pairs. Bell recognizes them as club membership, a sign that a gambler had been approved.
Sherlock and Bell visit the club and are stonewalled by employees who apparently speak no English. Sherlock sees a man mopping the floor, and points out by his expensive shoes that he is the owner hiding from them. When the owner claims that a man threw up, Sherlock points out how large the area was and that there are bullet holes in the concrete. Sherlock spots what appears to be a smoke detector, and recognizes it as a security camera. Sherlock views the footage, and notes that it took a while for the people to react. Sherlock deduces that the killer walked into the club unmasked, and put on the mask when he walked in. He views footage from another camera and sees the killer's face.
Tropes:
- Asshole Victim: Trent Annunzio used to abuse his wife on a daily basis for years.
- Brits Love Tea: Sherlock is put off when Joan serves him a cup of Chinese herbal tea that has medically proven benefits for people with colds.Sherlock: What is this? I asked for coffee.
Joan: Well, you asked for coffee, but you got tea.
Sherlock: No, I'm British, this is not tea. - Burner Phones: The phone used to contact Raul Ramirez is found in Brendan O'Brien's apartment which the police take as proof that he hired Ramirez. Sherlock points out that the whole point of a burner phone is that you get rid of it when you're done to avoid incriminating yourself. Holmes eventually works out that Trent planted the phone as part of his plan to frame Brendan and Jun for his death.
- Citizenship Marriage: Trent Annunzio drew in his apparent wife Jun by promising this, but refused to marry her so he could keep her under his control. Annunzio's assistant genuinely fell in love with her and after Sherlock solves the crime he and Gregson find a friendly judge who will rush through the marriage so Jun doesn't get deported.
- Eye Scream: Annunzio had both eyes shot out to cover up the fact that he had eye cancer.
- Foreign Culture Fetish: While never explicitly called out as such, Trent Annunzio (who was Caucasian) clearly had a serious obsession with Chinese culture that went beyond his academic interest. In addition to frequently visiting the country and playing in multiple mah jong parlors, his "wife" Jun was a Chinese woman who he abused using techniques developed by the Chinese secret police.
- Frame-Up: Trent Annunzio's Thanatos Gambit is intended to frame his teaching assistant for his murder and ensure that his wife is either arrested as an accomplice or at the very least deported from the United States. As Gregson notes, even after Sherlock has explained the scheme, it has been so well-planned that Sherlock needs more evidence to stop it from succeeding.
- The Illegal: Jun is forced to reveal she moved to America illegally because Trent promised to marry her once she arrived. Her confession means she almost gets deported before Sherlock and Gregson are able to intervene.
- Product Placement: At one point Sherlock goes through a lengthy demonstration of how to set up his Microsoft Surface Tablet and uses Bing to conduct a search. The fact that he's sitting on a toilet the entire time and is searching for a sex offender registry is probably a coincidence.
- Rewatch Bonus: Trent's complete lack of anything resembling surprise or panic in the cold opening before he is murdered and then the security footage is this - he hired the killer himself. He is, however, disoriented because his hired killer is carrying out the "hit" ahead of schedule and in a location other than where he planned for his body to be found.
- Sick Episode: Sherlock has a cold at the beginning of the episode. Researching the Chinese herbs Joan uses to make him some herbal tea allows him to recognise the traces found in Trent's stomach, and from there work out that Trent was using them to treat his eye cancer.
- Terminally-Ill Criminal: Trent had inoperable eye cancer that would have eventually killed him so he arranged his own murder.
- Thanatos Gambit: Trent Annunzio arranged his own murder to save himself from a more agonizing death and also to frame his assistant and wife.
- Villain with Good Publicity: Trent Annunzio was a respected professor of Asian studies at a well-known university, well-liked by his colleagues and students alike. He was also a sadist who kept his young wife prisoner in their home as a Sex Slave, knowing that she could not report him to anyone without being deported from the country and losing custody of her infant daughter.
- Wicked Cultured: Trent Annunzio spoke and read fluent Mandarin, which allowed him to teach Asian studies at a university, travel extensively in Asia, and participate in an underground mah jong parlor. It also allowed him to collect and interpret manuals published by the Chinese secret police, instructing the reader how to beat victims without leaving any marks, which he frequently used on his wife. Sherlock notes that once Annunzio realized he was dying, he turned his formidable intellect to planning the perfect Frame-Up against his wife and his teaching assistant who he'd learned was sleeping with her.
