Irene has a target on her back now courtesy of Jack, who wants the egg USB drive back. It’s decided that she should stay with Sherlock for the time being for her own safety, which means Watson has to move out.
The episode plays on Sherlock’s obvious attraction to Irene, as well as Irene’s general fitness as a domestic partner—she even gets him to eat ordinary food! She also has fun teasing him, because apparently when it comes to women Sherlock is thirteen years old.
The same goes for Kyougoku, who his head-over-heels in love with Maki-chan and has a plan to woo her that’s straight out of a middle-schooler’s mind. He places her on an impossibly high pedestal and showers her with gifts, including a diamond ring to hold her hand, but all Maki-chan wants is a boyfriend with whom to go on ordinary dates.
Maki gets her wish, and they eventually end up in a hotel, where Kyougoku presumably learns Maki’s secret down below. The outcome of this particular plot is ambiguous and not particularly compelling. That the success of Kyougoku’s plan somehow inspires Watson to serve as a lookout for Irene (once Sherlock’s place is ransacked and they move her to a former yakuza hideout)—it’s a bit thin, motivation-wise.
Much is made this week about him having nothing to do, which makes you wonder whether he’ll ever bring up his case with Sherlock, or if it’s a running gag that he never will. Matters are made worse by the fact Watson is terrible at keeping Irene safe. On her first night in the theater, she gets stabbed, while Sherlock runs after a decoy. He’s not even a good doctor, as he fails to administer any kind of first aid, but just kneels beside her, gawking.
It isn’t until later, when Sherlock gives word that Irene has died of her injuries, that Watson realizes Moriarty—who was with Irene just before he arrived—shouldn’t have known where Irene was. Many clues in this and previous episodes point to Moriarty as Jack. I’m also not convinced Irene is really dead. Sherlock may just be saying that in earshot of Moriarty because he’s already pegged the kid as the culprit.