Watch this first.

The first book by John Darnielle, the singer-songwriter who tours and records (with and without a band) as The Mountain Goats, shares its subject, more or less, with “The Best Ever Death Metal Band in Denton,” everybody’s favorite Mountain Goats song. The book, Black Sabbath’s Master of Reality, is the 56th entry in Continuum’s ongoing “33 1/3” series, each devoted to a single album. Darnielle’s conceit is to explain Paranoid’s sludgy follow-up in the voice of Roger Painter, a fifteen-year-old boy sent by his mother and stepfather to a long-term stint in a psychiatric hospital in the fall of 1985, for reasons having at least partly to do with his love of heavy metal. Deprived of his Walkman and cassettes, he explains and expounds upon his favorite record in mandatory daily diary entries.

“I thought if I could really show you how it felt to be listening to that music by myself in the dark… you would know what it is like in my heart,” says the depressed teenager after breaking into the nurses’ station to steal his Sabbath tape, in one of his many attempts at explaining how much better — how much more understood — he feels when he has someone to feel bad with. Later, he says, “The guitar tones and the thumpy thumpy drums soaking into me so hard… what I need in my life is to be liberated into feeling bad… What I need is a place where I can spray anger in sparks like a gnarled piece of electric cable.”

That Roger feels good about feeling bad is maybe the simplest way of saying that John Darnielle’s Black Sabbath’s Master of Reality is about light and its opposite — just as Darnielle’s career is about lightness and its opposite. (Light and lightness aren’t the same thing, at least not always, as we shall see.)