“Beware, there’s a chance we’ve left the real world and we’re now in David’s one.”

Melanie Bird utters this line in ‘Chapter 5’, and she proves to be correct and false at once. But the quote begs a question. Just what exactly is David’s world if David isn’t in control? Who is David if he’s playing home to another consciousness, and has done so since birth?

‘Chapter 5’ is where Legion starts to put some of its cards on the table, and reveal some clarity about the true threat of the series. It’s not quite the tour de force of last week, lacking that wall-to-wall experimentation and a feeling that there’s a surprise round every corner, as it’s more concerned with plot mechanics.

Yet it’s still an excellent episode that keeps Legion in a fascinating place as it heads into the final stretch of the season, and it’s all the more exciting and terrifying for the amount that it reveals and suggests about the bigger picture that this show has been hiding for so long.

What’s interesting is that the vision offered for David’s real enemy is so different from that of the pilot. The sinister Division forces were clearly marked out as the antagonist there, providing a tangible external threat for David to confront, while the Devil with Yellow Eyes was a sinister Easter Egg lurking in the background.

In case it wasn’t already clear that the villains had switched places, ‘Chapter 5’ makes it abundantly clear, with the Division left in gruesome, misshapen ruins while the Devil with Yellow Eyes asserts its supremacy over David and his entire inner circle.

That shift makes complete sense. The Devil is the embodiment of everything unknown from within the recesses of David’s mind, harnessing the abilities that David can barely even begin to understand to their fullest, devastating extent. As a force that’s completely separated from the physical world, it’s intangible and therefore impossible to pin down, cycling between myriad forms from Lenny to Benny to King to the devilish figure who personifies its evil.

It couldn’t be a more appropriate villain for a show where nothing is certain.

After the slow burn of the early episodes, Legion has reached a satisfyingly brisk pace in its storytelling, and that’s reflected in the substantial shifts in characterisation we see here beyond the personalities we were first acquainted with.

‘Chapter 5’ is predicated on exploring self-deception in all its forms, from David’s brashly hubristic tone to Syd’s increasing confidence in her new environment where she can finally indulge her impulses without fear of her power taking over to Melanie’s stubborn belief that she can keep David’s powers locked up and under control, informed by the pathos of her simple desire to have her husband back now that he finally seems within reach once more.

That means a more incisive examination of the flaws that false hope can bring about in these characters, with their own subjective viewpoint of reality overriding the cold, hard reality of the situation. In a way, everyone this episode is a little like David – locked up in their own heads.

There’s instantly a feeling from David’s very first scene in ‘Chapter 5’ that something is deeply off – a feeling that Legion actively cultivates with its weird, jarring soundscape and atmospheric use of colour as malevolent red light seeps into the pristine white room that David has built for himself as his own personal kingdom.

Dan Stevens’ excellent performance shifts from endearingly nervy to offputtingly cocky, and David’s typical need to be guided by others is replaced by a strange clarity of purpose. When Legion has to convert that innate feeling of wrongness into concrete action, it does so with devastating effect.

‘Chapter 5’ is the first real time that David unleashes his powers, though we barely see them in action – just enough for the episode to drive home that nagging, unnerving feeling right into active fear of what David is become as he embarks on his violent rampage with a callous spring in his step.

The aftermath of that rampage is grim and uncompromising as limbs protrude from ceilings and where piles of ash linger on floors as the soundtrack shifts into aggressive emotionality as opposed to the veiled score of the first half.

It’s a terrific subversion of the power fantasies that play out weekly on half a dozen superhero shows, reminding us of the coiled power that David holds within himself as it’s unchained by the Devil with Yellow Eyes, egging on David’s hubris to power past any of the compassion and empathy that typically defines our protagonist.

With the absence of the real David, the heart of ‘Chapter 5’ lives with the deeply human struggle of Syd, whose feelings are all too easy to understand and relate to, and all too difficult to solve.

Her fallacy is the irresistible temptation of feeling normal. Her story of her first sexual experience that she relates to David is a quietly disturbing and sad example of this – a desperate bid to enjoy the experiences of others that only reinforced her status as the outcast and the ‘other’.

Rachel Keller plays this scene with a poignant longing that makes it all too easy to understand her dismissiveness of the red flags in David’s behaviour, linking into a question that fascinates Legion – can identity exist if there’s no-one to reflect it back at you?

‘Chapter 5’ uses this question to point out the reason for Syd’s love for David, and also the reason why it can become truly dangerous: he is a reflection of her in that he shares her experience, but that means it’s all too easy to believe that they’re the same.

It’s an example of how Legion has threaded a difficult needle: it’s unashamedly cerebral and preoccupied with some complex theories of memory and identity, but with Syd, it’s found a sense of humanity through which it can express those themes. In doing so, it’s avoided the easy pothole that so many prestige shows of this ilk fall into, which is to become chilly and inaccessible with nothing for viewers to latch onto.

Noah Hawley accomplished this on two seasons of Fargo, proving his talent, but it’s impressive how easily it’s translated to a genre whose human relationships can often be robotically derived from a soulless formula.

For all the relatable humanity at the core of this show, however, it’s still capable of utterly bamboozling the viewer at every turn. The soundless sequence in David’s house is a great example of this experimentation, cranking up the tension and terror by robbing the viewer of the safety net of dialogue to explain and digest the situation.

Legion has increasingly adopted the tools of a horror movie to articulate its key threats, shifting from the psychological terror of the unknown to the gruesome horror of an obese yellow monster grinning as it bears down on Syd.

There’s no safe refuge in the real world for these characters as David’s mental abilities override any sense of safety in the tangible, but the mind, as this episode so clearly shows, is an even greater minefield of uncertainties and lurking terrors. There’s nowhere to hide at all from monsters who exist everywhere at once.

Except… The ending of ‘Chapter 5’ could suggest otherwise. In a mind-bending twist, we’re whisked back to Clockworks, the asylum where everything began, with the entire main cast dressed as inmates circled around Lenny the therapist.

Is this a refuge that David has created in his mind, using what he knows? Is it actually real, and what we’ve been seeing for the past five episodes has been a lie? Is anything real?

I think I need two brains to understand this show.

Aired at 9pm on Thursday 9 March 2017 on FOX.

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