The comic book "What if?" began in 1977 with a single question: "What if Spider-Man had joined the Fantastic Four?" (Turns out, he'd break them up.) Each issue began this way, with a new question that asked what would happen if some element of the Marvel Universe was altered in ways both large and small. Which allowed Marvel writers to tweak decades of Marvel mythology without damaging the sacred canon. In one issue in the 1980s, all existence is erased; the next issue, in a meta-twist, superheroes return to the planet and find themselves grappling with massive swaths of white blank pages to fill.

Clever stuff. Indeed, one of the issues ("What if the Avengers had never been?") is the plot of the third episode of the new Disney Plus series based on the comic. The basis of the next Thor movie — which finds the Norse god's ex-girlfriend (Natalie Portman) becoming a new Thor — can be traced back to issue No. 10, 1978: "What If Jane Foster had found the hammer of Thor?" As in the comic, the narrator is the Watcher, a kind of bulb-headed Rod Serling, an alien immortal who, as promised, merely watches, never interferes, offering only a vague chorus. He describes himself (voiced by actor Jeffrey Wright) as "your guide through these vast new realities." In the first episode, when the future of Captain America pivots toward something vastly different, he blurts "There! That's the moment!" In the second episode, when T'Challa, Black Panther-to-be, is kidnapped as a child by aliens who later became the Guardians of the Galaxy, the Watcher asks: Does our destiny determine our future? Or is it the nature of our world?

A cynic might say "What If ...?" is a ploy to extend the seemingly inexhaustible Marvel Universe to infinity and beyond. And sure, it is probably that. At times, it plays partly like that. But it also rarely feels cheap. Each question produces consequences. By switching Captain America's gender, a fresh host of new concerns float up. Kidnapping T'Challa as a child (then telling him Wakanda is a wasteland, to be forgotten) echoes the history of Black America.

All of which poses a curious problem for the "What If ...?" TV series (already OK'd for a second season): One of the hoariest truisms of pop culture is that it mirrors its times. Marvel itself found success in the early 1960s with characters who reflected issues of racism (The X-Men); Marvel's TV and films have found room for the surveillance state (Captain America) and even sexual abuse (Jessica Jones).

But who expected parallel-universe plot lines to compare with the real thing? For an audience watching a promising new TV series, it's where the fun begins: "What If ...?" is the inventive follow-up, a lesson in how storytelling is fundamentally decisions, big and small, all in a row. But in life, that's less fun. The Watcher introduces himself in the first episode of "What If ...?" as the guide to a "prism of endless possibilities." While taking notes, I wrote down a "prison" of possibilities and had to rewind a few times before I realized that he actually said "prism." It just sounded a little too optimistic to be true.