It’s a problem that seems to have begun with Mary (Amanda Abbington), introduced as John Watson’s fiancée in season three in “The Empty Hearse,” but then unmasked as a former superspy and freelance assassin in “His Last Vow.” That revelation tipped Sherlock from heightened realism into implausible, comic-book inspired fantasy, complete with a grotesque villain holed up in an architecturally splendid hideaway. The most ingenious scenes in that season showed Sherlock (Benedict Cumberbatch) retreating into his mind palace to reason his way through a series of head-scratchers. But, in the end, brawn triumphed. Sherlock, unable to defeat a tyrannical media baron through brainpower alone, shot him in the head, declaring himself to be a “high-functioning sociopath” in order to justify the act.

The moment seemed to crystallize Sherlock’s evolution (Mycroft’s “blunt instrument” comments came in a scene not long after). And season four’s three episodes have doubled down, focusing largely on the tribulations of the show’s main characters and nodding only occasionally at intriguing puzzles. It’s no coincidence that “The Lying Detective” was the best work of the season—it was the only episode that actually presented Sherlock with a substantial case, namely a monstrous millionaire moonlighting as a serial killer. By contrast, “The Six Thatchers” dealt almost entirely with Mary’s past before dispatching her to provide narrative trauma for Sherlock and John (Martin Freeman), while “The Final Problem” was a climactic mess, seemingly indulging the writers’ instincts to have a lark, consistency be damned. “You got a lot of actual plot for your entrance fee,” Moffat told Entertainment Weekly. “The final sequence running around trying to stop a plane crash, trying to solve a puzzle, and John Watson drowning — I just thought it was breakneck and fun.”

I wrote two weeks ago about being disappointed with Mary’s death, and wondering why such a brilliant show has such problems fitting intriguing female characters into its universe. The emergence of Eurus (Sian Brooke) as Sherlock’s secret sister in “The Lying Detective” seemed to signal how wrong this was, but the Eurus of “The Final Problem” was somehow a completely different character still: a bizarre mashup of the supernatural monster Samara in The Ring and Javier Bardem’s Raoul Silva, a wronged former ally intent on revenge, in Skyfall. Eurus, who played three distinct characters convincingly in a previous episode, was suddenly a horror cliché with lank black hair and dead eyes, using mind control to compel others to do awful things, and plotting extravagant riddles for her brother that put his friends in mortal danger.

Things got weaker still when the action suddenly shifted to Sherlock, Mycroft, and Eurus’s childhood home, a pile of stones as stately as Skyfall or Wayne Manor (both of those, you’ll remember, also ended up being obliterated by baddies bearing grudges). John, trapped in a well, discovered the bones of a child (another echo of The Ring), which led Sherlock to discover another memory he’d suppressed, along with any awareness of his sister. Decades ago Eurus, jealous of Sherlock’s closeness with his best friend, Victor, trapped Victor in a well and gave Sherlock a puzzle that would lead to him. But Sherlock couldn’t solve the riddle, Victor died, and Sherlock’s tormented psyche reimagined Victor as “Redbeard,” a dog, while also prompting him to shut down the human side of his personality and clinically investigate crimes for the rest of his life as penance.