Many a superhero origin story involves exposure to a volatile substance — something dangerous, radioactive, caustic — that can be powerful if mastered, ruinous if uncontrolled.

In HBO’s “Watchmen,” beginning Sunday, that fissile storytelling material is history: specifically, America’s legacy of white supremacy. The first episode begins with the 1921 riot in Tulsa, Okla., in which white mobs rampaged in the prosperous “Black Wall Street,” massacring African-Americans in the street and strafing them from above with airplanes. A small boy’s parents pack him onto a car that’s fleeing the mayhem, like Kal-El being sent from Krypton. But there is no Superman flying to the rescue.

With that opening, Damon Lindelof (“Lost,” “The Leftovers”) reframes the universe that the writer Alan Moore and the artist Dave Gibbons created in the 1980s comics series. Where Moore wrote an alternative history of Cold War America — a pre-apocalyptic dystopia in which masked vigilantes have been outlawed — Lindelof reaches back and forward in time to root his caped-crusaders story in a brutal American tragedy.

The choice invests this breathtaking spectacle with urgency. “Watchmen” is a first-class entertainment out of the box, immediately creating a sad and wondrous retro-futuristic world. It takes longer, though, to get a handle on the complicated and all-too-real material it uses as its nuclear fuel.