The fourth Harry Potter film is the pivot around which the series revolves, in oh so many ways. Most obviously, it’s book 4 of 7 — the halfway point. It’s also where the books switch from short ‘children’s novel’ lengths to the huge tomes they eventually became. More importantly, it’s the instalment on which the overarching plot of the entire series hangs. Although each previous entry in the Potter canon contributed something to the mythology (even if sometimes its significance wouldn’t become apparent until much later), they’re still viewable as discrete adventures. So too is Goblet of Fire, for the most part — the exception being its final act, which kicks off the story that will consume the rest of the series.

The film is no less of a turning point, for its own reasons. Note that this is when the films’ marketing began to emphasise the ageing of the actors: the teaser trailer begins with shots of Harry, Ron and Hermione from each of the four films; the promotional TV specials go behind the scenes not only on the new film but also its predecessors; clearly substantial retrospective interviews were conducted too: watch the Creating the World of Harry Potter: The Magic Begins documentary on the Philosopher’s Stone Ultimate Edition and it tells the story of the films’ birth by mixing interviews not only from the sets of the first film and the ‘now’ of the final film’s production, but also in costumes and on sets from the fourth movie.

It makes sense: at this point the series was moving beyond your stock franchise length of “trilogy” and into less frequently charted waters, amid speculation that the leads would be recast. With Goblet of Fire being the last point you could reasonably pull that off, I imagine it paid to emphasise that these were the same kids — that we see a cast age in more-or-less real time throughout their childhood, including many small supporting roles as well as the leads, is one of the Potter films’ more unique highlights.

The other big behind-the-scenes decision was one of length. As noted, this is the first Potter story to explode from a short children’s tale, which could be adapted in full in two-and-a-half to three hours, to a lengthy novel that would require masses of time to cover in full. Considerations of spreading it across two films were reportedly dismissed when director Mike Newell promised he could do it in one, essentially by cutting subplots and extraneous material — much as Alfonso Cuarón had on Prisoner of Azkaban, but on a grander scale. (Imagine if they hadn’t made that choice: instead of eight films, the Potter series would have sprawled to 11 instalments!) The result of such editing here is a very direct film, rattling through its plot — even with stuff cut, there’s still a lot of story to cover.

Said story concerns two foreign schools visiting Hogwarts for the Triwizard Tournament, a series of dangerous challenges, into which someone enters Harry against his will. It’s a nice clear through-line: a series of tasks, interspersed with investigations into who forced Harry to participate and why. It all comes to a head in one of the series’ most famous moments, the murder of Cedric Diggory. I can’t remember if Diggory’s meant to be a nice guy or an irritating jock, but here he’s played by Robert Pattinson, proving it’s not only his involvement with the Twilight franchise that makes him smug and annoying. Still, the impact of Diggory’s demise is still shocking and effective for those who don’t know it’s coming — this isn’t just a light series of children’s adventures any more. Of course, the death of a single-book supporting character is less impactful with an awareness of the franchise as a whole — there’s much worse to come, leaving this a mere opening move.

The other element that begins to creep in from this point is all the teenage romance stuff. Provoked mainly by the Yule Ball, with the guys having to pluck up courage to ask girls and dance lessons with teachers, the characters’ love lives start to become a notable factor. For all the plausibility and humour with which it’s depicted, there are times later when it will become a bit tiresome, especially in the novels. Fortunately, much of that’s internal monologue and subplot, and so goes astray here. Extra thanks to Mr Newell for that.

One of the more overlooked facets of Rowling’s work is her penchant for allegory and gentle satire. That’s understandable — they’re just Kids’ Books about magic, after all, and occasionally thuddingly written ones at that. Allegory you can take or leave (who’s really going to gain a perspective on HIV from Lupin’s struggle with lycanthropy?), but the satire is nice. Here it’s the press under fire. Rita Skeeter may have a greatly reduced role compared to the novel, but her Quick-Quotes Quill — which, essentially, just makes stuff up — is present and correct. The next tale, Order of the Phoenix, carries on this motif (the press demonise Harry), as well as setting its sights on blinkered and ineffectual government, and the evils of exam-focused impractical teachers. It’s all rather pleasing, actually, and you have to hope Potter’s millions of readers took it in and learnt something.

It’s easy to let certain events overshadow the entirety of Goblet of Fire; to subsume it into the single long narrative that arguably takes over the later stories. But though it puts broader events in motion, this is still a self-contained tale all its own — and one of the series’ most exciting at that, between storming action sequences and some effective twists. There’s a fair argument to be made that it’s the film series’ best entry.

In about a month, as I’ve already joined the Order of the Phoenix, uncovered the Half-Blood-Prince, and found both parts of the Deathly Hallows, I’ll offer an overview of the David Yates films…

Prisoner of Azkaban marks a significant turning point for the Harry Potter film series. Viewed now, it’s easy to see it as just Episode 3 of 8; a saga still getting underway. At the time, coming off the back of two incredibly successful films, it felt like a grand shake-up of an established formula.

It’s the first Potter to move away from a Christmassy end-of-year release slot, for one thing, debuting at the height of summer in May. That also made it the first to break the one-per-year release cycle they seemed to be aiming for, which would’ve emulated each film covering a single year of Harry’s time at school. The release date was only 18 months after Chamber of Secrets, but it had an impact — particularly to little Draco Malfoy, who seems to have undergone the majority of puberty in the short time between the end of Chamber and the start of Azkaban. I still remember my shock when he first appeared in the trailer — I thought they’d recast.

Most striking, however, is the new director. Alfonso Cuarón doesn’t ditch the faithfulness to J.K. Rowling’s novels that defined Chris Columbus’ opening pair, but he does ditch the slavishness, and brings a hefty dose of his own stylish directorial skill in the process. Azkaban is a fan favourite among Rowling’s novels, but Cuarón’s preparedness to change things when necessary made the film more of a hate object for some. The wider world had it right, however, because Azkaban was received as the best Potter yet and, I think, was the start of its rehabilitation from a fans-only series of Children’s Films to something that merited across-the-board full marks when Deathly Hallows Part 2 arrived seven years later.

Cuarón and screenwriter Steve Kloves (who would pen every Potter film bar the fifth) focus in on the novel’s plot, ditching its copious world-building and backstory asides. This has both pros and cons. In the former camp, it leaves room for Cuarón to make something more exciting and filmic than Columbus — you can’t imagine the craziness of the Knight Bus in either of the previous films. It also keeps things moving forward, at quite a pace too, rather than meandering off here and there. Even the Quidditch match serves a purpose.

On the downside, it strips away some explanations that not only deepen the series’ world but, in some cases, help it make sense. We never learn the identity of Moony, Wormtail, Padfoot and Prongs (makers of the ever-so-useful Marauder’s Map), or quite why Harry thought he saw his dad by the lake with the Dementors. The former is only nice detail, I suppose, but the latter event makes much more sense when you know the full explanation from the novel. The story gets by without it, but those unfamiliar with the book who stop to think about things may consider it a plot hole, or at least a leap of logic.

The film introduces two of my favourite characters from the series: Gary Oldman’s Sirius Black and David Thewlis’ Remus Lupin. In slightly different ways they’re both outsiders — underdogs, as it were, if you’ll excuse the pun — but both honourable and powerful… but not as pompous as that poor description makes it sound. The film series doesn’t treat either of them particularly well compared to the books, but then supporting characters and subplots are the first things to go (quite rightly).

The other big cast addition is Michael Gambon, replacing Richard Harris as Hogwarts headmaster Albus Dumbledore. Gambon seemed all wrong when he first turned up, replacing the previous near-perfect casting choice. He’s more familiar now, making it harder to judge which actor is superior; but it’s difficult to imagine Harris getting to grips with some of the cheekier and more active things Dumbledore is called on to do later in the series. Was the requirement to recast a blessing in disguise? Perhaps.

Azkaban was a breath of fresh air when it was released in 2004, really kicking the Potter franchise into life creatively. I know I gave the first two four stars each, but having since watched this and Goblet of Fire, the opening episodes pale in comparison.

Tomorrow, I put my name in the Goblet of Fire…