Another jaw-dropping episode from 'Sherlock' season 4 this weekend which saw this complicated sleuth meet the most evil man he has ever come across. And, potentially, the most evil woman. 'The Lying Detective' is the most intensely scary episode yet.

SherlockToby Jones stars as the villainous Culverton Smith in 'The Lying Detective'

So Watson (Martin Freeman) has a new therapist and he's having visions of his deceased wife Mary (Amanda Abbington) everywhere. That's what Sunday's (January 8th 2017) episode entailed. It turns out that she's having a good influence on him in the end, because it's her words combined with a frantic Mrs Hudson (Una Stubbs) who encourages Watson to help Sherlock (Benedict Cumberbatch) and forgive him for his involvement in Mary's death. 

Sherlock isn't doing particularly good either. He appears to be taking large amounts of heroin which is affecting his judgement terribly, though he's still fairly sharp when he receives a visit from one Faith Smith; the daughter of a famous philanthropist named Culverton Smith (Toby Jones) who has been using a newly manufactured drug which alters the memory on his associates so that he can confess his desire to murder without them remembering the conversation later. 

She remembers though. At least, she remembers that he wants to kill someone, and wants Sherlock to help her find out who. As it turns out, Sherlock believes there is no particular person because Culverton Smith is a serial killer. Meanwhile, Mrs. Hudson is at the end of her tether and tracks down Watson at his therapist's house, confusing him immensely with her Aston Martin ('For God's sake, I'm the widow of a drug dealer, I own property in central London and for the last bloody time, John, I'm not your housekeeper!'), the boot of which holds a trembling, handcuffed Sherlock. 

Watson agrees to examine him, though Sherlock has other things on his mind when he arrives at hospital for a meeting with Culverton Smith. (Everything seems to be happening in quick succession because Sherlock has managed to predict Watson's movements so precisely that he has arranged every meeting two weeks previously.)

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Smith is the hospital's major benefactor and his funds are the reason it is standing, which means he's allowed to wander around wherever he likes in the building (cue uncomfortable shudder when you notice disturbing parallels with Jimmy Savile) including the mortuary - his 'favourite' room. It seems like Smith is one step ahead of Sherlock, when his daughter Faith arrives and Sherlock discovers it's a different person completely to the one he met at Baker Street.

He ends up in hospital on a drip, recovering from his heroin overdose, and Watson leaves his old walking cane in the room. Culverton Smith arrives and tries to kill Sherlock by overdosing him on the medication that he's attached to and attempting to suffocate him, but Watson arrives at that moment to rescue him. Turns out that Holmes planned the entire operation after watching the final video message from Mary - the medication was actually saline, and he deliberately made himself ill so that Watson would re-connect with him, plus he even hid a recording device in the walking cane to tape Smith's confession.

However, that's not where this show ended. There's been whisper of the other Holmes brother Sherrinford all episode, but it's the sister Euros that they really need to worry about. She was the one who disguised herself as Faith in the beginning, she was also the woman that Watson had been flirtatiously texting, and she had taken the place of Watson's therapist (who's tied up in a cupboard in her own house). The final scene sees her shooting Watson in the head - but he can't be dead now, surely?