Director Sam Dunn is an anthropologist who wrote his graduate thesis on the plight of refugees. He’s also a heavy metal fan and, in this accessible documentary, sets out to explain that most maligned of musical genres to a mainstream audience.

Featuring interviews with Iron Maiden’s Bruce Dickinson, Slayer’s Tom Araya and many more, it’s both a robust defence of the music from its most articulate spokesmen (plus a few drunken buffoons such as Norwegian extremists Mayhem) and a condemnation of its darker side. But if you’re looking for This Is Spinal Tap, you’re in the wrong place. Everyone is treated with respect. Metal fans will love it, though actually liking the music certainly isn’t a prerequisite to finding A Headbanger’s Journey engrossing, horrifying and – yes – funny.