“It’s such a fine line between stupid and clever,” remarks faded rocker David St. Hubbins (Michael McKean). This Is Spinal Tap is a film that manages to occupy both sides of that line, being as it is a clever movie about stupid people. It is an enormously funny, well-crafted comedy, one of the very best ever made.

From the first frame the film blurs the lines between fiction and reality, opening on Marty DiBergi, the director of a documentary about rock band Spinal Tap, played by Rob Reiner, director of This Is Spinal Tap. Reiner spends little time in front of the camera here but he nails this particular character, making Marty an awkward on-screen presence who doesn’t know how to behave in front of his camera. In these opening moments he frequently crosses and uncrosses his arms, uncertain how to hold himself as he sets up the film for the audience. Marty has spent months on tour with Spinal Tap, a band with as much talent as self-awareness – much to the detriment of whatever dignity they have left.

The band is fronted by David St. Hubbins and his childhood friend Nigel Tufnel (Christopher Guest), the Lennon and McCartney of the band if The Beatles had been utterly ridiculous. Derek Smalls (Harry Shears) is on bass, Viv Savage (David Kaff) is on keyboards, and the drums are occupied by a revolving door of unfortunate fellows who have met various horrible ends, including choking to death on someone else’s vomit and succumbing to spontaneous combustion (“Dozens of people spontaneously combust each year. It’s just not widely reported”). Over the course of two decades the band has gone through various incarnations and had some success but their glory days are far in the past. Nevertheless, they set out on a tour to conquer the United States, convinced that they have what it takes to gain the adoration of audiences despite all evidence the contrary.

In the middle of the tour David’s girlfriend, Jeanine (June Chadwick), comes over from England, leading to tensions within the band. Nigel, especially, doesn’t like her and the way that she diverts David’s attentions and inserts herself into band business. She eventually succeeds in pushing Spinal Tap’s manager out of the picture and taking over his job, taking the bands fortunes from bad to worse in the process. Now instead of playing small, respectable venues the band is playing at air force bases and fairs where they get second billing to puppets. It would be sad were it not for the naiveté and indefatigable optimism of the people involved, who are just determined to keep on going.

The key to the film’s success is that it knows that its characters are dumb, but it never treats the audience as if they’re dumb, too. There’s a lightness of touch to its humour that requires the audience to pay attention and to be patient. Take the Stonehenge gag, for example, which unfolds in four parts. It begins with the band trying to come up with a way to get the audience excited and draw bigger crowds, and deciding to revive a popular showstopper from the past. Since the band never planned on revisiting the number, the set wasn’t brought on tour. Nigel insists that a prop can be made for the show and creates a crude drawing – complete with measurements – to be passed on to a set designer. The set designer then creates the prop which, to the shock of the manager, is only 18 inches tall, per the drawing. The show goes on with the absurdly tiny prop, the audience laughs, and afterwards the band discusses how it could have gone so wrong. Everything about this mini-arc is hilarious, but the icing on the cake is when Derek asks if he can put forward “a practical question”: Are they going to do Stonehenge again the next night?

What is accomplished by This Is Spinal Tap is rare in that it manages to mercilessly skewer its characters but also manages to avoid seeming mean. The film has a lot of fun with the dimness of the band members and their entourage, but it also obviously has a great deal of affection for them, as evidenced by the fact that they ultimately get a happy ending. The balance achieved is delicate and perhaps the result of the fact that the three stars – Guest, McKean and Shearer – and the director are also the writers, meaning that everyone involved in pushing the story forward is on the same page with regards to tone and comedy style. The result speaks for itself.

A trailer of Reiner’s mock Rocumentary: