Neophyte director Marty DiBergi unveils a captivating "rockumentary" that takes us on a journey through the North American tour of the aging rock band Spïnal Tap. The iconic trio at the heart of the group consists of David St. Hubbins, Nigel Tufnel, and Derick Smalls, joined by keyboardist Mick Shrimpton and a series of drummers who have faced bizarre, often fatal accidents over the years—ranging from spontaneous human combustion to choking on their own vomit.
As they prepare to promote their latest album "Smell the Glove," which controversially features a degrading image of a woman in bondage, their first performance at Madison Square Garden turns out to be a remarkable success. The band's record label CEO enthusiastically toasts to their achievements, remarking that they are "Tapping Into The Millennium," which also happens to be the title of their much-anticipated tour.
The documentary shifts to an interview with Marty DiBergi, who recounts the storied history of Spinal Tap, including their numerous lineup changes and notorious misfortunes faced by drummers—one, for instance, met his end in a particularly odd fashion. As the band travels to their next performance, they pass the time reading Sammy Davis Jr.'s autobiography, while listening to their unforgettable hit "Big Bottom," featuring all three leads on bass guitars. We also get a glimpse into how critics have received their discography, with their album "Shark Sandwich" notoriously receiving a curt two-word review: "Shit sandwich."
Their journey takes a challenging turn at the Recording Industry Convention in Atlanta, where they confront canceled gigs and backlash over their album cover. With their marketing team outraged and calling the cover "filth," a heated argument ensues with the record label's CEO, [Bobbi Fleckmann](Fran Drescher), who describes the album cover as "sexist."
While awaiting their performance in Chapel Hill, North Carolina, Nigel expresses his deep frustration over the horrific food being served, questioning how anyone could expect them to perform under such conditions. The band performs "Hell Hole" to a warm reception, yet their troubles continue as a mishap during equipment transport results in another canceled gig in Charlotte due to insufficient advertising funds.
Back with DiBergi, it becomes evident that Spinal Tap's fanbase is shrinking. Once playing to arenas of 10,000 to 15,000 seats, they now find themselves relegated to much smaller venues, a decline that their manager, Ian Faith, dismisses as nothing significant. In a moment of frustration, the band wrecks their hotel room, and the next day, [David’s](Michael McKean) girlfriend, [Jeanine Pettibone](June Chadwick), plans to visit as the band finds unexpected solace in a radio play of their old song "Listen To The Flower People"—though it's bittersweet when it's presented during a "where are they now" segment.
In a comedic twist, the band visits Graceland and attempts to pay tribute to Elvis by performing "Heartbreak Hotel," though they hilariously struggle to remember the lyrics. As they navigate another gig in Milwaukee, they face disappointment when the record label decides to scrap the controversial album cover for a bland all-black design.
Concerns escalate backstage during their performance when [Derek](Michael McKean) becomes trapped in his prop pod, leading to a string of embarrassing incidents, including a last-minute record signing in Chicago where no fans show, leaving them dejected. Their next performance takes an odd turn as they find themselves opening for a magician at a child's birthday party in Albuquerque, further exacerbating tensions within the band.
Throughout it all, Jeanine introduces her costume ideas, but [Nigel](Christopher Guest) resents her interference. The over-the-top performance of "Stonehenge" turns into a comical disaster when a miniature replica descends from the rafters, leading to chaos as dancers almost topple it.
A heated argument with [Ian](Tony Hendra) breaks out after several tour blunders, prompting [David](Michael McKean) to suggest they reconsider his management. As they gear up for a performance at the Miramar Air Force Base, they face indifference from the crowd, culminating in [Nigel](Christopher Guest) storming off.
As the tour wraps up in Stockton, California, they scramble to create a setlist without [Nigel](Christopher Guest), leading to a strained performance that leaves little to no lasting impression on the audience. With the tour officially over, David and [Derek](Michael McKean) discuss new projects and the surprisingly lucrative prospects ahead.
Ultimately, [Nigel](Christopher Guest) surprises everyone by reappearing, revealing that their song "Sex Farm" has made a significant impact overseas, particularly in Japan. With a chance for redemption on the horizon, the band reassembles and plays "Tonight We're Gonna Rock You Tonight," leading to a triumphant finale with cheers from a massive Japanese audience. As the curtain falls, both hope and revitalization loom, suggesting that perhaps Spinal Tap's story isn’t quite finished yet.
