Synopsis for 4×12: Fiona returns and expresses an interest in Sherlock, which leaves him torn. An undercover narcotics detective gets killed before a grand heist can be completed, leaving Joan and Sherlock to figure out why.
Fiona, the coder from earlier in the season, got back in touch with Joan while Sherlock was still working on investigating his father’s near-murder. She wanted Joan’s assistance regarding her new boss. Given that her last one had been a criminal and used her code for nefarious purposes, she worried that her new boss would also be a criminal. She asked Joan to look into him for her.
While busy with that, Sherlock got called into the station to talk to a Captain from Narcotics. He was worried about a case they were working and had been persuaded by Gregson to request Sherlock’s help. There was an undercover detective who had successfully infiltrated a meth trafficking gang and they wanted to make the final play against them. In their base of operations was a laptop containing all of the information about their accounts, their buyers, their shipments, and their members. They wanted to get the content off of the laptop, but the big issue was that it was stashed in a private, locked office.
So what did they need Sherlock to do? Oh, you know, help orchestrate a heist. He agreed to it almost immediately. After all, Sherlock doesn’t tend to turn down serious puzzles.
Sherlock began working on the case almost immediately and created a replica of the base using a dollhouse in order to understand what he was up against. While he did that, Joan walked in and shared about her visit with Fiona. She had agreed to do the background check. Sherlock, on the other hand, had it in his mind to meet the undercover detective and securing that meeting ended their conversation rather abruptly.
When Joan met back up with Fiona, she explained that her new boss appeared to be a good man. He gave to charities, had no criminal background, and there was nothing in his history to suggest that he was anything but above board. That seemed to assuage Fiona’s fears, and she handed Joan a first edition of a T.S. Elliot book. At first, Joan thought it was a thank you gift but Fiona explained that she was just returning it to Sherlock. He’d allowed her to borrow it after the case when he walked her home to make sure she was alright.
Sherlock met the undercover police officer and received all the information he needed to proceed with the plan. Invigorated, he moved all of the furniture up to the roof in order to create a walkthrough of the heist for practice. He had to figure out how to best get the detective through to the end of it. Joan was not amused, especially when she realized her bed had been lugged up to the roof too.
Unfortunately for Sherlock, the heist was called off when the detective turned up dead. They immediately raided the base and took in all of the men who were there at the time. The only person who didn’t make an appearance was the leader, Nick Farris, and they began the search for him.
It didn’t take too long to find him, and they brought him in for questioning. Their interrogation didn’t yield much, though. There had been body cam footage of the shooting and whoever had shot the detective had a mole on his hand that would identify him. Nick Farris didn’t have that mole, and also mentioned that he had as much reason to find the guy who did it as the police did. After all, he’s the one who brought the police down on Nick’s operation. He “hoped they’d put them in the same cell,” since he had a lot to talk about with him.
Sherlock was back to square one.
Joan returned home to return the book that Fiona had given her and accused Sherlock of having romantic interest in Fiona. She knew for a fact he hadn’t owned the book before giving it to her, meaning he’d bought it specifically for her. What followed was essentially a game of “Sherlock and Fiona sitting in a tree.” He got frustrated and tried to dismiss himself from the conversation.
They received the detective’s autopsy which concerned Sherlock. They immediately went to the morgue, Fiona momentarily forgotten, and found that that detective had a mole on his wrist. He somehow had shot himself. They had to figure out why. More evidence soon surfaced showing that someone had drained all of the gang’s accounts after the raid, but before police picked up Farris, which put them on the trail of an accomplice.
Joan and Sherlock had another conversation about Fiona and he admitted to finding her attractive, and being drawn to her. However, he worried that she would be “more sensitive than most women” and was scared to try and initiate anything for fear of hurting her. He didn’t have a particularly good track record with relationships, so it wasn’t really a surprise he was hesitant when a relationship could potentially be about more than sex.
Back on the case, their suspicions turned toward a detective who worked in computers that had been giving them information. They knew whoever the accomplice was walked favoring their left leg and could only be about 5’ 7” and the detective, Lisa Hagan, fit the bill. They just had to figure out how to prove it since there had been absolutely no evidence at the crime scene.
Fiona stopped by to bring Joan a thank you gift, as she’d decided to give her code to her new boss. Her real reason for stopping by, however, was to see Sherlock “because she liked talking to him.” She told him she finds him handsome, and asked if he wanted to kiss her. He hesitated, and that seemed to tell her all she needed to know for the moment as he was pulled away by work.
Joan woke up the next morning thinking Sherlock had moved her bed to the media room. In reality, he’d moved the media room into her bedroom. He’d figured out, through a rug that was supposed to be at the scene but seemed to be missing, that the detective and Hagan had worked together to recreate the office where the laptop was. They were going to stage the whole thing, force the NYPD’s hand at a raid, and then have the laptop land in Hagan’s hands where she’d be able to drain the gang’s accounts and split the profit 50/50. She decided to really kill him and take the whole profit.
They easily found the set she’d used and brought her in to present her with the information. There was no going back. Case closed.
The episode concluded with Sherlock visiting Fiona. He admitted he did find himself interested in her and asked if the kiss was still on the table. She told him no, she had needed it then but didn’t need it at the current moment. They settled instead on going to get coffee together because they are beautiful awkward babies.