If this is the world that the existence of superheroes have created, then that butterfly must have flapped its wings pretty hard.

When the incident ends in a cop’s getting shot up by an assault rifle, the Tulsa police, led by Chief Judd Crawford (Don Johnson), find themselves facing a renewed terrorist threat. The Seventh Kavalry, an organization that parallels those original masked avengers, the Ku Klux Klan, has been waiting in the weeds for a while, but now they’ve resurfaced in homemade Rorschach masks. (Rorschach, the narrator of the graphic novel, operates with a brutal moral certitude that connects with the far right.)

Crawford calls on his department to take on the threat, but they have to conceal their identities, too, or risk bloody reprisals on their doorsteps. The cops are both official and clandestine administers of justice, a contradiction that the show has only just begun to explore.

One powerful answer to the Seventh Kavalry problem is Detective Angela Abar, a.k.a. Sister Night (Regina King), whose superhero get-up is like a ninja version of the nun costume Zoë Lund wore to shoot up a Halloween party in Abel Ferrara’s “Ms. 45.” Born in Vietnam — which in the “Watchmen” world became the 51st state after the God-like Dr. Manhattan turned the war in America’s favor — Abar has ostensibly retired to run a bakery. But it’s a front for her job on the force and the extracurricular activities that go along with it. Her abduction of a Seventh Kavalry lowlife from a trailer park gives Crawford and the department’s interrogator, Looking Glass (Tim Blake Nelson), the jump on a terrorist enclave at a cattle ranch.

The coordinated assault on the cattle ranch, echoing the many real-life showdowns between the government and heavily armed separatists, is a good early example of how this first episode of “Watchmen” delivers on ideas and spectacle in equal measure. It’s a superhero show, after all, and the pitched battle against the Seventh Kavalry counterbalances the Tulsa massacre nicely, suggesting a continuity of racial violence across a century. (It also brings down “Archie,” the owl-eyed ship from the comic, in a blaze of glory.)

The final shot ends the episode with more questions: Crawford, hanging from an oak tree, and below him an enfeebled mystery man in a wheelchair (Louis Gossett Jr). In his hand he holds a note, last seen in the episode being carried by a black child who escaped the riot a century before. “Watch Over This Boy,” it reads.