Synopsis for 4×16: The Baskervilles are found to be an unlucky family when one of the heirs falls to his death after being chased by what appears to be a mysterious hound creature. Sherlock and Joan are on the case though, even as Sherlock helps the Medical Examiner, Eugene, come to terms with his budding drug problem.
To kick the episode off, Sherlock visited with Eugene, the medical examiner who has worked a lot of cases for them. They’d found his DNA in what was supposed to be a sample of a killer’s DNA for a case they were trying to close. Of course, Eugene wasn’t the killer. Rather, he accidentally contaminated the sample with his own DNA, rendering it useless and setting the case back. He looked guilty, Sherlock looked concerned.
Elsewhere, a man out in the woods finds himself engaged in a dangerous pursuit. The audience is not given a clear view of what exactly is chasing him, but he runs right off of a cliff to his death in order to get away from it.
Sherlock and Joan ended up on the case because the victim’s brother approached them due to his father’s connection to Sherlock’s father. The man who had died was a Baskerville, part of a very affluent family. The remaining brother, Henry, wanted to hire Sherlock to investigate his brother’s death. He offered to pay well, so Sherlock and Joan accepted it and started in on their investigation. They surveyed the woods where the situation occurred and Sherlock believed that there was a witness to the events.
Joan was able to track down the man who had seen it, and he was a homeless gentleman. He said what he’d seen was a giant wolf chasing the Baskerville heir down. The whole episode was a lovely callback to the classic The Hound of the Baskervilles story.
Sherlock visited Eugene again for their chess match, and found his chess partner to be lacking. He expressed his concern, especially over the amount of anti-anxiety medication Eugene appeared to be taking. Naturally, Eugene became a bit defensive over it and didn’t want to admit he was having trouble. He was dealing with it the way he deemed appropriate, and essentially told Sherlock to stay out of it and not worry. He was taking care of it himself.
The team turned to a company producing genetically modified organisms that Charles Baskerville, the dead brother, had ties to. They thought perhaps his investments had something to do with his death, and that someone had been angry enough to kill him. There they found a genetically modified dog that glowed, but the team insisted that dog had never left the lab. There’s no way it could have been the beast that chased Charles off of the cliff to his death. The staff there put them on the trail of a man who had been leveling threats against Charles and the company. It turned out to be a dead end though, as there was no way the man in question would have ever been able to give chase to Charles.
Their next clue led them to another company that rivaled Charles’, but he insisted he had no motive to kill him. He supposedly had a patent of some sort for a super soldier dog, but explained that the dog had never come to be. It had been stalled out in the early stages of the project and abandoned. Rather, they should be looking at people that Charles had “patent-jacked,” which was the process of buying up a company and taking the patents he wanted before letting the company dissolve.
While talking with the living brother, Henry came under attack. There was some sort of beast out in the yard that he heard and Sherlock, with some quick thinking, insisted that he go around to the other side of the pool. When they arrived at the scene, they found Henry had done just that and in the pool was a four legged robot that had every intention of killing Henry. It hadn’t been programmed to understand something like a tarp over a pool, so when it walked across the tarp it fell into the empty pool and was trapped.
They looked at what companies would have produced the robot and they turned toward Stapleton Innovations. It just so happened that the head of it was a Baskerville cousin, and the third in line for the Baskerville fortune. With the death of Charles and Henry, he would have been the heir. However, he claimed he had an alibi: he’d been on a hunting trip, and anyone could have stolen the robot from their fleet. It came to light through one of his employees after the meeting, however, that his “hunting trips” were actually cover-ups for stays with prostitutes and everyone was actually covering for him.
Sherlock tracked down Eugene to approach him again about his tendency for self-medication. He opened up to the other man about his own troubles, and how he had been dragged into a never ending self destructive spiral and didn’t want Eugene to go down the same path. It showed a lot of growth on Sherlock’s part, both as a person and as a recovering addict, to reach out and remain consistent in order to help someone else who was struggling. Eugene seemed unsure about it and they parted ways.
They brought in Stapleton and questioned him, and he insisted that even though he’d lied about his alibi, he wasn’t the one who killed them. How would he prove it? He’d punch a cop, in front of witnesses, and get convicted. Apparently the Baskerville trust was only available to heirs without felonies. A felony conviction would render the claim to the trust invalid, and he was willing to give it all up to prove that he was not the one who did it. They believed him.
They ended up looking through the entire family to try and find someone else with a claim. When that was fruitless, they decided to bait a trap: “kill” off Stapleton. They’d have Henry orchestrate it, so that Stapleton was dead and Henry would be convicted of a crime which would disqualify them.
Then whoever orchestrated the whole thing would probably show up to claim their prize. It worked, and a young woman who actually worked for Stapleton turned out to be a not-so-distant relative who wanted to claim the loot. However, it was quickly revealed that she had fallen for a trap, and both Stapleton and the remaining Baskerville brother called her out on it.
She was taken into custody, the case was solved. Eugene, after it was all wrapped up, showed up on Sherlock’s doorstep. He had files in his hand, possible replacements for his position. He wanted to let Sherlock have his top pick, because he knew whoever it was would have to have a high tolerance for Sherlock’s oddities. He admitted that he did have a problem, and that he was going to go on medical leave for a time to try and figure things out. Sherlock encouraged the choice, and they both had a touching moment.