Holmes has two roosters that he saved from a cockfight because he wants to see if he can train them to be less bloodthirsty. He succeeds, and he also gets Watson to say something dirty about cocks. It's not much of a subplot unless you like chickens.
In the actual plot, a bomb was set at a lunch table containing some bankers and government agents. The investigation is complicated by the presence of Gareth Lestrade, last seen taking credit for Holmes's work in London. Now he's the personal security advisor for the CEO of the bank that lost some vice presidents in the explosion, and he's getting on Holmes's nerves by claiming he's a consulting detective. He's got an assistant called Ms. Truepenny who thinks Watson is trying to steal her job by sashaying around in front of Lestrade.
The investigation has more false trails than usual. They start with a waiter who went home early that day and seemed to hate the customers, but Holmes rejects him as being small-time. A famous bomber takes credit, but Holmes thinks the manifesto was not philosophically sound. The CEO that employs Lestrade turns out to have checked into the hotel the day before the bombing under a lavishly fake name, so he becomes the focus of the investigation. He's played by Bill Irwin (of whom your recapper is a big fan), and Holmes learns that he was spying on one of the people killed in the explosion.
After leaning a bit on Lestrade, Holmes learns that the reason is that the CEO likes to pick out random people and give them large sums of money to have sex with him, and he makes Lestrade do the negotiations. Lestrade is ashamed about that, but Holmes just finds it mildly weird, not appallingly decadent. Now that the CEO and Lestrade are basically cleared, Holmes takes a little time out to discover the name of the legendary bomber. But when the police find him, he's recently killed himself with a chlorine gas bomb, so never mind. Then a blackmail demand comes in, and Holmes realizes that everything was orchestrated by one of the people that survived the bombing, because her government job let her see a report ahead of time.
The CEO doesn't want to have her arrested, because it will mean his expensive and decadent practices will be public. But Lestrade has found his morality and insists that the murderer be punished. And so she is. And now Lestrade lives at the Brownstone, because he's been fired.
We start under a table. There's a bomb and it explodes. That moved along quite quickly!
Watson comes home to discover that Holmes has adopted some roosters in order to stop a cockfighting ring. Well, he stopped the ring, but then there were these two roosters just standing around with metal spurs, not doing anything. He wants to train the combative nature out of them to prove some kind of point about how good he is at training animals. Watson is uninterested, so Holmes asks if she has an aversion to cocks. She doesn't want to indulge him, because it's now clear that he's just doing this so he can say "cock" a lot. Luckily for them both, Gregson texts them to tell them about the explosion.
Outside the Griffin Hotel in the snow, Gregson briefs them. People from the Treasury and Labor departments were trying to sell people from the big banks on the new budget proposals. The bomb was homemade, but intricate.
Inside, Holmes looks at the carnage and recreates the scene. Two of the people that were killed were vice presidents of a bank called Whitbrook-Balsille. This is relevant because Richard Balsille, the CEO, has a security czar who insists on access to the crime scene as well as the investigation. Holmes claims he doesn't work with czars. But he's already worked with this one, because it's Gareth Lestrade! In this incarnation of Sherlock Holmes mythology, Lestrade is a bad person who was last seen claiming credit for Holmes's work. He kisses Joan's hand, which is weird. Then he asks Holmes if he's ready to match wits, which is the sort of thing you say when you're a supervillain. He's mostly acting like a pompous jerk.
Holmes takes pictures of the crime scene while Lestrade has fresh coconut water brought to him by Miss Truepenny, an aspiring consulting detective who acts as his assistant. I will tell you right now that "Miss Truepenny" is her actual name. Lestrade goes on about how he's a big media star who has invitations to do DOUG Chats. That's this world's version of TED Talks. Holmes is pretending not to pay attention. Watson says her friend from St. Bede's informed her that the two survivors are conscious and available to be interviewed. This seems like something that should have come through police channels, doesn't it? The cops have just completely washed their hands of this case. Lestrade runs off with Miss Truepenny in his wake. Now that he's gone, Holmes admits that he's heard of DOUG Chats; he just didn't want to encourage Lestrade. Which is reasonable, because he's apparently going to be taking the corporate helicopter to go eight blocks to the hospital.