His Last Vow was a fitting ending to series three (Picture: BBC)

Sherlock resorts to extreme measures to defeat blackmailer Charles Augustus Magnussen in the series finale, His Last Vow.

[Warning – major spoilers] Steven Moffat provides a fitting ending to series three, as a twisting, intrigue-filled plot sees the defeat of one nemesis followed by the return of another.

‘I’m not a hero, I’m a high-functioning sociopath’

The first two episodes of this third series have proven divisive among the show’s fans, as more humour and the introduction of Mary marked a shift from plot-driven stories to more relationship-based ones.


Now we know why Moffat and Mark Gatiss pursued this route. The lightness of the opening episodes was needed to offset the darkness of the finale. Yes, there are humorous moments, but none of the whimsy particularly evident in The Sign of Three.



MORE: Sherlock fans in a frenzy after he gets a girlfriend

Mary’s role has been pivotal in helping to define Sherlock and John’s evolving friendship. Here she becomes a significant player in the central story and the first in a series of pressure points which allows Magnussen to gain leverage over Mycroft.

Mary was a central player in the final story (Picture: BBC)

MORE: Sherlock series 3, episode 2, The Sign of Three – wedding bells and a new direction

Ultimately Sherlock’s final, shocking act is a product of his vow at the Watsons’ wedding to always be there for them. It’s an indication of the extent of his friendship that he does not hesitate to sacrifice himself for them – an emotional reaction which neither Mycroft nor the pre-fall Sherlock could have countenanced.

The power of information

In many ways, the creepy and charmless Magnussen is an even more chilling nemesis than Moriarty, both being mirror images of what Sherlock might have become.

The creepy and charmless Magnussen (Picture: BBC)

From his position as a media mogul, he acquires compromising evidence on people, which gives him the power and wealth to gain even more information and therefore influence. That’s a notion which strikes a chord with modern-day concerns about surveillance and personal data.

By contrast, John finds his power by burning the USB drive containing details of Mary’s past. In doing so, he unburdens them both.

For Magnussen, knowledge is power. For John, the absence of knowledge is freedom.

Misdirection aplenty

Moffat’s script contains a stream of misdirections from the opening scene right up to the closing one.

Initially we are led to believe Magnussen accesses his vaults via a Google Glass-like display in his glasses. Only at the climax do we discover it’s all just a visualisation of his own mind palace.

MORE: It’s only January but Sherlock is the best thing on TV in 2014

We’re also teased by Sherlock’s romantic relationship with bridesmaid Janine, ultimately a means of gaining access to Magnussen’s office.

There he mistakes Mary for Lady Smallwood. Mary incapacitates rather than kills Sherlock – indeed, her immediate 999 call saves his life – as he uses his mind palace to maximise his own chances in a beautifully executed sequence.

Sherlock mistakes Mary for Lady Smallwood (Picture: BBC)

Holmes’ dummy at Leinster Gardens turns out to be Watson. And Sherlock’s treasonous theft of Mycroft’s laptop is also a ruse.



Finally, as Sherlock is flown away on what promises to be a fatal mission, the series’ theme starts to play before fading out to reveal the true cliffhanger: the seemingly impossible return of Jim Moriarty.

There’s something about Mary

The writers hinted in the previous episodes that Mary was not what she appeared to be. It’s enough for Sherlock to deduce the past she has tried to leave behind.

Remember also how she recoiled at the mention of ‘Cam’ in a telegram at the wedding? She recognised it as ‘C.A.M.’ – Magnussen’s initials. And her ‘I’m panicking’ at the evening party was less shock at her pregnancy than the realisation that her window for eliminating Magnussen was closing.

So now we know she’s a former CIA agent and assassin. Her skills might come in handy in tackling Moriarty.

Where next?

His Last Vow delivered a jaw dropping final five minutes (Picture: BBC)

If the question on everyone’s lips at the start of this series was ‘How did Sherlock survive the fall?’, now it’s ‘How did Moriarty survive his suicide?’ Cue up the fan theories again!

Series three of Sherlock has brought us a different tone, greater depth to Mycroft’s character and the introduction of Sherlock’s parents.

But Moriarty’s survival provides the most significant departure yet from canon. Will series four see the partnership of Sherlock and John permanently expanded to include Mary? And will we see the show increasingly diverge from the original stories?

After an uneven run-up to the finale – I loved The Empty Hearse and was underwhelmed by The Sign of Three – His Last Vow barely missed a step, ramping up the tension steadily and delivering a jaw-dropping final five minutes that few could have predicted.

Am I thrilled at the prospect of Holmes and Moriarty locking horns again? Of course I am. Series four cannot come soon enough.