The mind is a terrifying thing.

Just how well do we know ourselves, exactly? Can our formative memories be relied upon, or have we filled in the gaps with fiction that softens the truth? Can we really separate ourselves from our past mistakes?

None of those questions have any definitive answers, and that’s pretty terrifying.

Now imagine you’re someone with an unimaginable power you can’t even begin to understand, having been told that you’re either a paranoid schizophrenic or, more recently, the world’s most powerful moment.

Oh, and the chances are that there’s another force at play aiming to rip your mind to shreds and will happily do the same to anyone who’s trying to help you.

That’s the story of ‘Chapter 3’, which turns Legion into a full-on psychological horror movie. It’s true to say that the season’s plot is continuing to burn slowly with revelations coming at a drip feed, which might test the patience of viewers looking for something more plot-driven as the season heads towards the halfway mark with relatively little revealed about the threat of Division 3.

Nonetheless, Legion’s precise understanding of tone, character and themes is creating something that’s intoxicatingly weird, but emotionally engaging and accessible.

The episode benefits from an increased understanding that a balance needs to be struck for Legion to make the best use of its unique elements. The showpiece moments of David’s power or of non-linear storytelling have a much greater impact this week because they sit alongside much more conventional drama of Syd and David’s budding relationship, or of the refreshingly blunt honesty of Jean Smart’s Melanie who seems more keen in keeping David on the same page this week.

When those moments come, communicated with evocative and powerful imagery such as David and Syd suspended in a flash of light, they hit hard, because Legion takes the time to build up a sense of reassuring clarity quite frequently throughout the episode before destroying it with another disorientating display that no-one truly has a handle on events.

‘Chapter 3’ also demonstrates a much more straightforward handling of David’s character arc, as his murky past is revealed while the idea that his ‘therapy’ in the present will cure him of all of his turmoil comes under significant scrutiny.

To do so, Legion takes a much-needed step back on the vicarious perspective of David’s world and points out how little we know about David, even in contrast to his limited self-understanding.

He’s someone who’s desperately tried to distance himself from the events that formed who he is today due to the light they put him in, and his journey in ‘Chapter 3’ is about his attempt to acknowledge that he can’t make a clean break from his past – that there’s still a little bit of the nihilistic junkie or the institutionalised mess left in him even as he strives forward with Melanie’s help.

It also helps that he has Syd as a contrast. Syd is David’s literal mirror image – she has a concrete sense of her own identity, but possesses a power that ensures that she’s come to disregard the importance of her body given how easily it can become a vessel for someone else’s soul.

‘Chapter 3’ adds another fascinating thematic layer to their relationship as it uses their opposing powers to question just how individual identity is formed if both mind and body can become disconnected from one another, and it contributes to the growth of what’s turning out to be a very effective love story that’s defined by refreshingly straightforward emotion that contrasts with the complex themes at play.

It demonstrates how Legion has struck a difficult and precise balance. It’s often baffling and disorientating, and it’s typical to come out of an episode wondering what the hell is going on story-wise.

Yet it’s never impenetrable, as Legion avoids the trap of becoming clinical and emotionally chilly as many unconventional psychologically-driven shows can do, and ensures that the existential and psychological questions it’s posing are clear for all to see – it’s the answers that are the problem.

That tension comes to a head in the defining sequence of ‘Chapter 3’, which is the final descent into David’s mind. As Syd hops between stages of David’s life in pursuit of him, journeying through his memories, Legion indicates its command of visual storytelling to illustrate the formative power of the past in shaping the present and showing the delusion of David that he could ever airbrush and block out these horrific events that defined him.

And pretty quickly, as soon as that delusion is revealed, ‘Chapter 3’ takes a sharp left turn into horror movie territory.

There’s two antagonists at play in ‘Chapter 3’ – the papier-mache ‘World’s Angriest Boy’ and the yellow demon of past episodes, and it’s impossible to pin down who either of them are, or what they want, which is exactly what makes them terrifying.

Michael Uppendahl, the episode’s director, uses all of the horror movie tricks in the book from flickering lights to abrupt jump scares to claustrophobic shots of the characters walled in by David’s mind, but it’s the psychological component of the horror that really makes this final sequence.

It’s an attack of everything David, and Legion itself, has refused to explicitly acknowledge, reminding us of the depths of David’s mental turmoil and of the obstacles that he can’t comprehend yet.

The yellow demon, in particular, becomes an even more unnerving threat here as he attacks Syd and Melanie after crawling out from a glowing crack in the wall in David’s memory, making it abundantly clear that this isn’t a manifestation of David’s fears – it’s something external with its own nefarious agenda at play that seems pretty indiscriminate in its aggression.

The culmination of it all is a cliffhanger that’s encapsulated in the endlessly suggestive final image of David mobbed by a legion (sorry) of faces as he’s trapped in the recesses of his mind. It’s the perfect place for Legion to go as it dives even deeper into its psychedelic exploration of David’s bottomless mind.

After all, as ‘Chapter 3’ shows so well, there’s nowhere scarier for David to be trapped…

Aired at 9pm on Thursday 23 February 2017 on FOX.

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