THERE’S a storm coming. A girl and her dog are caught up in it. The dog isn’t a little black terrier, it’s a great big Alsatian. The storm lifts them up into the air. They are not in an old wooden house, they are in a Land Rover. The girl and the dog land in a strange world and there’s a road up ahead. It isn’t made from yellow bricks, it’s made from yellow dust – opium. This world is Oz, but not the one you know.

The reason the familiar elements of Oz are so mixed up is that this is not actually The Wizard Of Oz – it is Emerald City, a new TV drama that takes the popular story, and the even more popular 1939 movie starring Judy Garland, as the starting point for a strange retelling, a reboot. The central parts of the story you know are there, but they've been darkened and twisted. Hence the yellow road made of opium. And the scarecrow isn’t a scarecrow – he’s a man who’s being crucified. The flying monkeys have also been turned into mechanical surveillance drones. As for the Wicked Witch of the West, she is a louche, gothic madam with Chrissie Hynde make-up and a serious substance abuse problem.

The series, which is being shown on 5STAR and stars Joely Richardson as a harder-edged version of the Good Witch Glinda, was bound to get off to a good start because we are all deeply familiar with The Wizard Of Oz. And that means we can enjoy spotting what the producers have done with the bits of the film we remember. The rainbow decoration in a window, for example. And the red gloves that take the place of Dorothy’s ruby slippers.

An Oz spin-off like Emerald City is not an original idea however. In fact, no single film has inspired more spin-offs, sequels, remakes, reboots, tributes, pastiches and satires than The Wizard Of Oz. It is, by far, the most culturally influential and important film ever made, way ahead of any of the films that might even come close – Star Wars for example or Psycho maybe. The songs in The Wizard Of Oz, its vocabulary, its iconography, the lingering images – beautiful and frightening – and, for some, its deeper, more profound meanings are part of a shared language of film, fairytale and childhood. In the last few days we’ve even seen it in the reaction of Storm Doris hitting the UK. As people tried to explain the consequences of the storm on Twitter, they chose pictures of Dorothy caught in the twister. It is a reference we all know. We get it.

But why? Why is The Wizard Of Oz so important and influential? When you think about it, it’s a pretty weird film to gain cultural significance: a farm girl ends up in a land run by a wizard and witches; she befriends a scarecrow, a man made out of tin, and a lion with no courage; and she ends up killing two of the witches before returning home using a pair of magic shoes. What is there about such a strange, surreal story about the pretty girl, and her little dog too, that connects and lasts?

Partly, the film is memorable because it has been shown on television so often – in the 1960s and 1970s, a tradition developed in the US and the UK of showing it every Christmas. It’s also easy to forget how frightening the film is for young children – and fear is one of the best ways to lay down lasting memories. When I asked around my friends and family for memories of The Wizard of Oz, the biggest theme was fear. There’s the wicked witch of course, but one friend told me his brother had to be taken from a screening in the 1960s, tearful and screaming, when Dorothy encountered the talking trees. Another said she couldn’t bear Dorothy’s predicament and the menace of Oz and hasn’t watched the film since because of it.

On a happier note, the film’s music has a large part to play in explaining the film’s popularity. The songs were composed by Harold Arlen with the clever and witty lyrics by EY Harburg – the man of genius who rhymed “rhinoceros” with “imposseros” and “hippopotamus” with “top to bottomamus”. The songs are funny and playful (“We hear he is a whiz of a wiz if ever a wiz there was”) but, in Somewhere Over The Rainbow, poignant as well. Watch Dorothy singing that song in the sepia farmyard and you can’t help wondering what kind of meaning it had for audiences in 1939 just as the Second World War was starting. You can also see, and feel, in those lyrics about a place “where dreams you dare to dream really do come true” the experience of every teenager who feels like they’re not listened to and who thinks there might be a better life somewhere else, or with someone else, or as someone else.

It’s the message of that song – which was nearly cut from the film by the way – that many believe is the core of The Wizard Of Oz’s popularity and the reason it has got deep into people’s heads. The filmmaker and critic Mark Cousins is a fan of the movie and has been campaigning for a blue plaque in Edinburgh in honour of George Gibson, the Scot who painted many of the backdrops in the film. He firmly believes it is all about the teenage experience.

“The Wizard Of Oz is about being young and having an adventure,” he tells me. “It's important that Dorothy is wide-eyed and yearning. It's 'Young Adult' fiction before its time. When you are a teenager you sometimes want to go into worlds you don't understand. The Wizard Of Oz is a masterpiece of that. It's great teenage art.”

This may explain why so many of the films, novels and graphic novels that The Wizard Of Oz has inspired are subversive. Such as the 1970s musical and film The Wiz, which turned The Wizard Of Oz into a celebration of America’s burgeoning black culture. Or The Lost Girls, Alan Moore’s 1991 hippyish, anti-war graphic novel which featured Dorothy having sex with the farm hands who turn out to be the scarecrow, lion and tin man. Or the 1992 science-fiction novel Was by Geoff Ryman, which features a troubled and disturbed Dorothy and a gay man who’s obsessed with the original film. The film has also been a noticeable influence on subversive filmmakers such as David Lynch and John Waters – and possibly George Lucas, the creator of Star Wars. (Does Lucas’s story about a girl who runs off with a metal robot, a scruffy boy, and a creature with a big mane of hair ring any bells?)

The first episode of Emerald City also has a pretty subversive take on Oz. Near the end, the wizard addresses the people of Oz and tells them why he is the right man to lead them. “If it were not for me,” he says, “Emerald City would have fallen like many of the great cities of Oz. I will protect you from the forbidden magic.” In the time of Trump, it’s obvious what’s going on there, especially when the wizard goes behind a screen and takes off his ridiculous wig and we get to see the little man behind the flames and smoke. Pay no attention to that man behind the curtain.

However, it’s the novel, Was, and the character of the gay fan, that touches most on a particularly important reason for The Wizard Of Oz’s long-lasting power, at least with a certain part of its audience. Almost as soon as the 1939 film was released, people began using “friend of Dorothy” as a euphemism for "homosexual" and the film has always been loved by gay men who, as young boys, are attracted to the movie without realising why. I sometimes wonder if it’s all down to that moment when Dorothy emerges from the grey house into the bright, musical world of Oz – she’s suddenly in a more colourful and exciting place; she’s escaping the restrictions of home; she’s coming out. Judy Garland herself, of course, is also a gay icon so that’s going on too: on top of the story of Dorothy yearning for a better life is the real story of Judy’s life going horribly wrong.

Mark Cousins can see the appeal of the theory, but thinks it’s all a bit bigger than that. “Oz is all those better places, all those utopias, all that longing for Bowie or magic or transcendence,” he says. “Yes, it feels like coming out, which is lovely, but it's bigger than that in a way. In The Wizard Of Oz, Dorothy takes a risk. She impresses herself. So often we disappoint ourselves. She doesn't.”

So is that the real point of The Wizard Of Oz: the fact that the central character is a young woman who spectacularly fulfils her potential? Gita Dorothy Morena – note the middle name – is a psychotherapist and the great granddaughter of Frank L Baum who wrote the original Oz novels, and she believes the film’s story is all about the power of the feminine. “Dorothy goes in as a woman, asking questions,” Morena has said. “She’s wanting to find her way back home and I think that’s a very feminine approach to a confrontation. She shows us the strength of the feminine.”

And have you noticed something else about Oz? It’s a matriarchy, a land run by women, apart from the Wizard himself of course but he’s quickly exposed as a useless little man pretending to be something he isn’t, a pile of humbug – and Dorothy is the only one, in the end, who is willing to stand up to him. The feminist interpretation of the film would also help explain one of its most famous spin-offs: Wicked, the 1995 novel and blockbuster musical which refuses to see the Wicked Witch of the West as a villain. But, as with any of the theories, there are other ways of looking at it: can a film in which a beautiful young woman destroys a faded, ugly, bitter old witch really be feminist? And listen to what Glinda tells Dorothy: “Only bad witches are ugly”.

Glinda also delivers what is supposed to be the message and moral of the film when she tells Dorothy that all she needs to do to get home is tap her ruby shoes together and say: “There’s no place like home.” I remember seeing that as a child and thinking: “Are you kidding? Dorothy gets the chance to get away from home to an exciting, colourful land and she goes back to Kansas to live with her nagging aunt and uncle?” For me and others, it’s the one bit of the film that doesn’t sound true – in fact, I’d rather it wasn’t there at all. “There’s no place like home” feels like a cheesy, conservative message tagged on to the end of a subversive film – a film, after all, that in the paranoid America of the 1960s was accused of being Marxist because of its whiff of revolution and the fact that ordinary characters like the straw man and the scarecrow end up running the place.

Mark Cousins loves playing around with these theories but says there are dangers in them too and in trying to dig too deep into Oz in an effort to explain it. “It had some metaphors in it but doesn't try to be too clever,” he says. “It leaves a fair bit unsaid which, as we know, is attractive. For all its colour and expressivity, it's gnomic and childlike. This is very likeable and open to interpretation.”

But for me, it still feels like it’s all about that song near the beginning, Somewhere Over The Rainbow. It’s not in Technicolor like the rest of the film, and the scarecrow and the witch are nowhere to be seen, but even so it sounds like the point of the film. Yes, Glinda might burble on about home being all that matters, but just look and listen to Dorothy singing Somewhere Over The Rainbow and you realise that Glinda has missed the point and the film is about something else entirely, something most of us feel at some point. It’s about looking over the fence, and down the path. It’s about pining for something different and realising that, in the end, you have to go and find it. That’s the point of The Wizard Of Oz. That’s why it has lasted and has meaning. It’s about leaving home. Whether you ever come back again is up to you.

Emerald City is on 5STAR on Tuesday at 10pm