Last week hinted at the return of Moriarty, or at least her syndicate as she is currently incarcerated (on at least two shows, no less, if you happen to also watch Game of Thrones). So when a guard and one of Morland's underlings are murdered at his building and then a bomb goes off, Sherlock and Watson swing into action in search of whomever has taken over Moriarty's dealings. Turns out it's a professor with business connections to rival Morland's—and also the father of Moriarty's daughter.
Joshua Vikner is his name, and he tells Sherlock and Watson they are "untouchable" because Moriarty has strictly forbidden any harm come to them. This does not seemingly extend to Papa Holmes however, and the reason for these assassination attempts remain a mystery. Is it really just business? Why so long ago and then now? Is it only because Sherlock is just now beginning to investigate the attempt on his father, the one that killed Sabine? Is he (or Morland) getting too close to something?
Meanwhile, Morland is moved to a safe house but not out of the city. I suppose he insisted on staying close to see what came of it all. He's keen to find who did it and put the screws to him despite Sherlock insisting his father allow the justice system to do its work.
The on-site murderer is our Russian friend, the one who'd skipped out of the gulag or whatever he'd been in. He gets captured then murdered before he can tell anyone anything of value. But is Vikner (the professor) behind that? It's all pretty convoluted.
Vikner, in fact, attempts to sue for peace between his organization and Morland's. But Sherlock—the would-be intermediary—doesn't bite on the offer. He's not interested in anything under the table; he wants old-fashioned justice in the form of police and courts. Seems he should know better than to believe that can be had when dealing with people who function so entirely outside the law and by their own rules. Is there an odd streak of naiveté in him, some weird optimism? Or is he that confident in himself versus these others?
The episode ends, however, with Sherlock and Watson walking into the brownstone and being faced with a bomb, so . . . Pride goeth and all that.
Season finale next week.