The episode begins at a crime scene where Bell tells Holmes that the two men who are murdered worked for ZBZ Securities and they had a contract for the museum. But Bell tells them that there is nothing missing from the museum. Holmes wants Watson to analyze the scene and state her deductions. Watson is taken aback; but she quickly gathers herself and tells him that the men were chased on to the parking lot and then shot. But the direction, in which the killer ran off, cannot be determined. Holmes tells her that there was no chase at all. Judging by the uniforms, Holmes tells them that one of them is a bad man posing as a guard and the other one is a real security guard.
He then checks the pocket contents of the bad man and finds some car registration receipts. This means that the bad man finds out the addresses of the rich men with an expensive car and steals from their houses when the owners are out. The real guard must have seen this guy lurking around and then they ended up shooting each other. He then checks the last dialed number; it is the burglar’s partner named Loco, who is presently robbing a house. Next, a driver walks up to Holmes and introduces himself as Crabtree. He works for Gerald Lydon of the Lydon Industries. Gerald has a proposal for Holmes. He tells Holmes that he has dementia. He tells them that he is suffering from hereditary cerebral amyloid angiopathy (CAA). Lydon tells them that somebody “gave” this to him and he wants Holmes to find out who did it.
Holmes thinks that since it is hereditary, he had to be born with it. He refuses to take the case. Later, at home, Crabtree arrives with a bribe; a bee that is known to make exquisite nests with flowers. Holmes is fascinated; but he still does not accept the bribe. Next day, Gregson tells Holmes that they have arrested Lydon for shooting his driver Crabtree. Lydon tells them that he doesn’t remember; but his nurse, Ms. Tompkins witnessed the whole thing. Lydon’s sons, Carter and Josh arrive but they are not allowed to see their father. Holmes arrives with the bee box in hand and tells Watson that he is taking this case. He then tells her that they will be going to the genetics lab that confirmed his condition. At the lab, they meet Ralph Keating, the President and Natasha Kademan.
Natasha has written several books. Holmes tells them about Lydon’s condition and Natasha tells Holmes that there are seven scientists who could crack the case. One of them is Ingvald Moller, and he runs a lab in Oslo. Holmes has found out that Moller has done extensive research on rare genetic disorders and recently has bought property which costs a fortune. His loan papers were co-signed by Carter Lydon. But Holmes wants to go to Oslo and question Moller. Just then he gets two texts and he realizes they are from Natasha and he feels that Natasha knows what is going on. Natasha agrees to meet them at the lab. But when they reach the lab, they find Natasha dead on the floor. They find blood splatter on the portrait hanging on the wall and Holmes thinks it is the killer’s blood.
Natasha’s fiancée arrives and tells them about Benny Cordero who was in prison. Natasha had used his blood without his permission. He suspects Benny. At home, Holmes is working on the molecular pattern that Natasha texted him. The next morning, Watson cracks the mystery behind the molecule. She took some help from her genetics professor Jerry. She tells Holmes that this is a man made molecule; it is a mutagen. It can be targeted at the gene that is responsible for CAA. Next, Watson goes to the dry cleaners and gets four sweaters. Holmes asks her to meet him at the station; Benny is found. But Holmes tells them that Benny is innocent. He feels that this crime is far more elegant and a sociopath like Benny has no place in it.
Holmes and Watson talk to Carter and they want access to their servers. Josh arrives and tells them that their father is declared incompetent and they no longer require their services. Watson makes up a story of a contract and Josh signs the papers and gives it to her. But he doesn’t take his pen back. Watson tells Holmes that they can swab the pen for Josh’s DNA. Holmes has taken Carter’s comb for his DNA. Bell calls Holmes and tells him that Benny’s DNA is a match to the blood found at Natasha’s murder scene and that they are booking him for murder. Benny tells them that he has an alibi. He was clicking pictures of his neighbor having sex, so that he could blackmail them. He feels that he is being set up.
At home, Holmes wants Watson to visit the dry cleaners once again. Watson goes to the dry cleaners and notices that they don’t know how to do business and also that there are six high end security cameras at the shop. She arrives home and tells Holmes about it. But Holmes is having a video conference with the six geneticists that Natasha told them about and according to them one can fake a DNA. The crime lab tests 13 loci against the countless loci present in a DNA. And according to the geneticists, these 13 loci can be faked. Holmes then tells her that he called in a favor and got Benny’s blood sample from the crime scene and one of the geneticists tested it; it had only 13 loci. So someone who had access to Benny’s blood created a sample with only the 13 loci he knew that the police would check.
Holmes tells Watson that there was only one person who pointed them towards Benny Cordero; Natasha’s fiancé, Paul. Paul is a geneticist and has an access to a good lab. They interrogate Paul. Paul admits that he killed Natasha. He tells them that Natasha and he got themselves tested for the warrior gene and it turns out that Paul has it in him; this means that he is a sociopath. Benny too had the same gene in him and Natasha had used his blood sample for testing. Paul realized that Natasha was avoiding him and moving on with a guy named Lincoln Dunwoody. He could not tolerate that and so he killed Natasha. But he also states that he has nothing to do with poisoning Gerald. He does not even remember what CAA stands for. Holmes then focuses on the name Lincoln Dunwoody.
He figures out that they are two different last names. The two families are great philanthropists and the patriarch of the Lincoln family, James Lincoln suddenly retired because he was diagnosed with CAA and there is no history of that disease in his family. Holmes feels that Natasha was not having an affair; she was trying to solve the mystery. But there is more; a woman named Greta Dunwoody dropped off from the society pages and also as the President of her family organization. No one knows why. It also appears that the family gave 20 million to a hospital. They go to the hospital and find that Greta does not remember anything; she is suffering from CAA. Holmes deduces that someone is giving rich people CAA so that they could get grants flowing in.
Holmes tells Watson that the Lyndon family donated a lot of money to Watt Helix, Natasha’s company. Watson thinks that Natasha was the whistle blower. The killer was someone powerful and capable enough of doing the same; Holmes main and only suspect is Brian Watt, the owner of Watt Helix. They interrogate Brian. Holmes and Watson deduce that Brian who is a decorated physician had CAA and was trying to work something around his condition. The research wasn’t going fast enough; so he had to plan a way to getting bigger money for his research. So he poisoned the rich people. The three victims were patients at the hospital where Brian held special privileges.
He injected the chemical through the IV. Case Closed. Next, Watson arrives at the dry cleaners. Bell is with her. The shop is a way for the smugglers to clean their money. Everyone at the shop is arrested. Watson arrives home and asks Holmes as to why he didn’t tell her that she was right about the fact that there was something wrong about the shop. Holmes tells her that he wanted her to trust her own instincts. The episode ends.