If this story wasn’t true, they’d have to invent it. Indeed, they already did. “This is Spinal Tap,” one of the most outrageous, influential, and utterly hilarious movies ever made, is a “mockumentary,” a fake documentary about a heavy metal rock group on a disastrous tour in support of a disastrous new album. “Anvil: The Story of Anvil” is an actual documentary about an actual heavy metal rock group on a disastrous tour in hopes of making a new album and it is hilarious and touching and completely captivating.

Like all great documentaries, this is the story of a passionate dream. Guitarist Steve ‘Lips’ Kudlow and drummer Robb Reiner (not to be confused with one-b Rob Reiner, who directed “This is Spinal Tap”) met as teens in a small town near Toronto and have been performing together for four decades. They had a brief brush with success in the 1970′s, when they performed at a festival with acts that have since gone one to sell hundreds of millions of CDs, and their Metal on Metal album is considered seminal to the genre. But for some reason, they never made it despite subsequent alliterative albums like Worth the Weight and Hard n Heavy. The eternally optimistic Lips has a day job delivering school lunches. But when a European fan calls to say she has booked them on a tour, they drop everything and go. Everything goes wrong. But, as Lips says, at least they have a tour for things to go wrong on.

There are some nice little bows to “Spinal Tap” — a producer whose amps go to 11, a drive by Stonehenge. And the inspired title lets you know from the beginning that it is cheekily subversive, even of its own pretensions. It never takes itself or the band too seriously. But the passion of its characters for rocking out hard and for the partnership they share is perfectly suited to rock as the ultimate affirmation of life in the face of The Man in all forms, from club managers who don’t pay to recording executives who don’t get it to time that goes by too fast. The support of their families and their unquenchable commitment to the music is ineffably moving. It is funny and surprising but filled with heart.