Holmes is teaching Watson to be a detective! That mostly takes the form of making her guess what's going on before he corrects her. For example at the top of the episode, she thinks somebody shot two security guards. But what really happened is that they shot each other, because one of them was an impostor. He also sends her to a dry cleaner's several times until she deduces that they're involved in smuggling and human trafficking.
The main plot involves a rich philanthropist with a hereditary disease that causes dementia. He's convinced he's been poisoned, but nobody takes him seriously, since the disease is hereditary. And causes paranoia. But after he shoots his chauffeur, Holmes takes the case and starts talking about visiting Norwegian geneticists.
There's one lady geneticist who wrote a monograph Holmes owns. It's about the Warrior Gene, which indicates sociopaths. She sends a text suggesting that she has useful information, but she is inconveniently killed. This leads to a sidetrack where it could have been a guy who hated her and was known to get stabby. But it was really her fiancee, who went to the trouble of making blood with fake DNA markers to implicate the other guy. He did this because he thought she was cheating on him, but the name he thought he heard was really two giant charitable trusts.
When it turns out that those two trusts also had super-rich people recently struck down by the rare hereditary dementia, Holmes gets back on track with the regular case. After consulting with all the top geneticists in the world, he establishes that it's possible to create a poison that could cause it. He helps lead Watson to the conclusion that the only reason someone would be doing this is if they were trying to increase the amount of funding pointed toward curing this particular disease. So it's this one particular geneticist named Peter Watt. Case solved!
We have a crime scene in the middle of the road! Bell explains the situation: the victims work with ZBZ Security, but nothing's missing from the museum. They're left with two dead bodies lying on the ground. Holmes declines to answer because he wants to make Watson do it. She's tentative, but she says each of them have been shot in the chest one time. The scuffs on the road suggest they chased the suspect. But no! Holmes says that one guard's ZBZ patches are handsewn. And his clothes are new. What was in his pockets? Four car registration cards with the owners' addresses. Holmes explains that the guy was finding expensive cars, then breaking in to find the home address of the owner. Then he'd call his associate to rob the place. There's also a cell phone and Watson knows the last called number will be the associate. He's named "Loco Maurice," which I love.
Walking down the street, Holmes tells Watson not to be discouraged, because detection is not just a skill -- it's a point of view. She should be alert to the bizarre and unusual. Like this stretch limo, with the driver staring at them. His name is Crabtree and he was referred by a Mr. Musgrave. He works for General Lydon, who has a proposal. I have to write all these names down because you never know when one of them is going to turn out to be important at the end of the episode. Holmes and Watson enter the limo, where Lydon and Miss Tompkins (his associate) are waiting. Lydon is a little twitchy; he's kind of acting like Robert Downey Jr.'s version of Sherlock Holmes. He says he owns eighteen patents and can do eleven pull-ups at age fifty-eight. But his problem is that he has dementia: Hereditary cerebral amyloid angiopathy. Watson translates this as "hereditary CAA," which seems like cheating. Anyone can sound smart if they just acronymize whatever they just heard. Lydon feels that someone has purposely given him this disease, even though it has "hereditary" right in the name. Watson points out that paranoia and delusions are symptoms of CAA. Holmes thinks the most likely explanation is that it's naturally occurring, so he won't take the case. He asks Crabtree to pull over.
Upstairs in the brownstone, Watson adds a book to a pile in the hallway. Downstairs, Holmes is pouring acid on a doll. Watson says she has no questions about her reading, although Jeremy Bentham -- as a philosopher -- has nothing to do with being a detective. Holmes says that free will is the cause of criminal behavior so Bentham is completely relevant. The door buzzes. It's Crabtree! He has a hexagonal box with a special bee in it. Holmes is very impressed by the bee, but he declines the offer. Crabtree says that he said Holmes would do that.