In the middle of the otherwise straight-laced Davison era, lies Snakedance – an exotic, experimental and slightly deviant experience. It feels like an illicit treat, like a sneaky spliff before heading back into English class, focussing on Eliot or Blake. It’s got much to say about expanding your mind to see the true nature of things. But let’s start with its most famous scene, which focuses on an elaborate but mysterious hat.

It’s a hat from the old times of the planet Manussa and it’s in the possession of this planet’s chief fusspot Ambril (John Carson). The hat features five sculpted faces in an outer orbit around its crown but is confusingly called “the six faces of delusion”. Not even Ambril, an antiquities scholar, knows why. It’s left to the Doctor (an excitable Peter Davison) to point out that the missing sixth face belongs to the hat’s strong necked wearer. Ambril, who had put the numerical discrepancy down to his ancestors’ inability to count rather than their ability to balance oversized headwear, is outraged to have this pointed out to him and orders the Doctor out.

Critics of this scene have mentioned that it’s a pretty obvious conceit and it’s surprising that Ambril and his fellow Manussans hadn’t worked it out themselves. Fair enough, but it’s also saying something else about them: that their minds are closed to symbolism, metaphor and nuance. Snakedance tells us that the Manussans are a decadent, complacent people, but that scene shows how bereft of imagination they are. They are blind and deaf to the threat of the return of the Mara – the ancient evil that once dominated their planet – because they can’t conceive of it happening. Just as they can’t imagine a situation where five faces can become six. They cannot open their minds to the possible.

Opening one’s mind to new possibilities and engaging in mind altering experiences to see the truth of things are at the heart of this enigmatic story. It starts with a dream, in which companion Tegan (Janet Fielding) has a premonition of arriving at the snake’s head cave on Manussa where the Mara will attempt its return. Later, the Doctor will hypnotise her and have her regress to childhood in order to confirm his diagnosis that the Mara is resident insider her head. In both these states, it’s shown that the only way to reveal the Mara is to suppress your own ego and enter into a subconscious state.

Once on Manussa, Tegan is mentally overtaken by the Mara, as she was in Kinda, this story’s prequel. Possessed companions are standard Who fare, but Tegan’s is something different because the Mara’s presence suggests not just suppression of her personality but an amplification of darker characteristics lying latent within her. This makes the Mara a uniquely disturbing creation: greed, lust, envy, wrath are all magnified by the Mara. It makes Tegan’s experience feel like a genuine expansion of the mind, in a deeply malevolent way. And to reinforce that this mind expansion opens up new ways of seeing things, there are symbols of distorted perception dotted around, like crystal balls and fairground mirrors.

Altering your mind also eventually proves to be the only way to prevent the Mara’s physical return to Manussa. This is the only Doctor Who story to place mystical, almost heroic significance on the “dropout”; the person who turns their back on society to travel into the wilderness, and search for life’s essential truths. Maybe with the help of drugs; the image of a mind blowing trip in the isolated wilderness seems to be what the snakedance actually is.  We only ever see one snakedancer, Dojjen (Preston Lockwood) and we never truly meet him. He turns up in a series of unexplained close ups which are dotted through the story and reappears at the end as the Doctor’s spirit guide to chaperone him through his own bender.

Dojjen used to hold the same position as Ambril, that of dusty historian and bureaucrat, but he dropped out of Manussan society to wander in the desert. Ambril dismisses Dojjen as a “crank”, one who “decided his particular line of research was best pursued up in the hills with a snake wrapped round his neck.” But Snakedance positions Dojjen not as a spaced out loon, but as the wise man from whom the Doctor must seek advice. He’s a bit like K’anpo in Planet of the Spiders, except that Dojjen is completely outside the establishment, and he’s a drug user. OK, so he doesn’t actually drop acid but his drug is the venom of the snake and he convinces the Doctor to sample it as well. And so we have the only Doctor Who story where the Doctor takes a mind altering substance in order to solve the story’s problem.

The insight the Doctor gains from the experience is to find the “still point” within himself. When the Doctor returns to the snake’s head cave to confront the Mara, he finds dozens of Manussans in thrall to it, paralysed as the Mara feeds off their mental energy, in order to take corporeal form. The question is how to prevent it and the answer, again, is to change mental states.

It’s never fully explained what the still point is, but what the Doctor seems to do at the end of Snakedance is to meditate, to eradicate conscious thought and therefore starve the Mara of the energy it needs to fully emerge. All around him, the gormless, weak willed Manussans are entranced by the Mara, unable to clear their minds and disbelieve it out of existence. Again, they lack the ability to open their minds, to mentally adapt to the world around them, which has suddenly got very dangerous very quickly.

This is why, I think, Snakedance is such an intriguing story. But it’s also a languid one. Its big moments are not action sequences, but ones which focus on characters changing their consciousness in order to expand their perception. They are personal, internalised events. In fact, the standard Doctor Who runaround bits – your chases through market places, dashes back to the TARDIS, the interminable Part Three lock up – are its least interesting segments.

It’s a story hampered by having to remember to be Doctor Who, as reinvented in 1983 as a cut-price action adventure serial. But despite all of that, writer Christopher Bailey manages to slyly – even covertly – tell a story with a deeply Doctor Who moral: a lack of imagination leads to stultification and corruption, but open your mind and you’ll be enriched and rewarded.

Plus you’ll know how to interpret a mysterious hat. So there’s that too.

LINK TO Thin Ice: fairgrounds and tattooed men.

NEXT TIME: It’s reality TV gone feral in Vengeance on Varos. And cut it… there!