Critic’s Notebook:  ‘Agents of S.H.I.E.L.D.’ is a true television marvel

Of all the creative and genre-expanding shows to debut in the last few years, none have been quite so fascinating to watch as the wildly ambitious narrative experiment of ABC’s “Marvel’s Agents of S.H.I.E.L.D.�

The hype explosion that prefaced its debut last fall — Joss Whedon’s return to the small screen! Possible cameos by “The Avengers� cast! — led to an underlying assumption that the show would either hit big or fail spectacularly.

It has, in fact, done neither. Struggling to find big ratings and, during early episodes, a consistently compelling storyline, “Agents of S.H.I.E.L.D.� ends its first season Tuesday having created a vivid alternate universe populated by some memorable characters (Ming-Na Wen’s crazy-great Agent May in particular). Not surprisingly, the show was recently renewed for a second season.

More important, it created a whole new sort of television show: One that must support, and change with, the plot twists of its film family.

Film and TV have always been kissing cousins, with stories, concepts and characters migrating back and forth. “Friday Night Lights� is the most oft-quoted example of a TV show outshining the film on which it was based. “Parenthood� and, more recently, “Hannibal� have also expanded a story made famous by film, while “Fargo� provides a more tonal, and quite unique, accompaniment to the movie with which it shares a name.

But never before has television been literally married to film, charged with filling in the back story and creating the connective tissue of an ongoing film franchise.

Debuting in the aftermath of the Battle of New York as depicted in “The Avengers,� “Agents of S.H.I.E.L.D.� resurrected Clark Gregg’s Phil Coulson to help the world cope with its new super-hero awareness. With a team that includes fighter pilot/martial arts expert May, the square-jawed Agent Ward (Brett Dalton), the adorable science/tech team of Fitz (Iain De Caestecker) and Simmons (Elizabeth Henstridge) and super-hacker Skye (Chloe Bennet), Coulson tracks down nefarious aliens and humans alike.

Although rife with mentions of the Avengers, and featuring a few brief cameos — most notably by Nick Fury (Samuel L. Jackson) — early episodes had only a same-universe relationship with the film franchise: “Thor: the Dark World� film was acknowledged by the team cleaning up the mess and then helping the Lady Sif (Jaimie Alexander) track down a rogue Asgardian.

Then, in March, “Captain America: The Winter Soldier� premiered and blew the show apart.

The revelations that S.H.I.E.L.D. had long been riddled with agents of the dreaded Hydra, resolved in film by a climactic showdown between Captain America and said Winter Solder, became the cataclysmic through-line of the remainder of the season. After every member of the team suspected the other, Ward turned out to be the traitor, while the rest found themselves without an agency and suddenly at odds with the established forces of justice. (The good news: Maria Hill [Cobie Smulders] is back in a big way.)

Tuesday night, presumably, debts will be settled, Nick Fury will be found and the construct of the next season will be set.

Until whatever happens in the next Marvel film shakes that up as well.

Rather than deep-sixing the series, the film’s revelations infused “S.H.I.E.L.D.� with a new energy, and helped explain, perhaps, why the show took so long to find its footing — in the writers’ room at least. The ground was literally shifting beneath its feet.

Never mind the middling ratings. That “Agents of S.H.I.E.L.D.� was able to succeed as a story both independent and ancillary is all but miraculous. Something ABC appears to be acknowledging with the announcement of the upcoming “Marvel’s Agent Carter,� based on a character from “Captain America.�

Following the adventures of Peggy Carter (Hayley Atwell), the woman Steve Rogers left behind, “Agent Carter� will have a historical time frame (post WWII) and a limited relationship with the ongoing film series, dealing instead with the quasi-feminist themes that drive period shows as diverse as “Mad Men� and “Downton Abbey.�

“Agents of S.H.I.E.L.D.,� on the other hand, is now not only a very good show in its own right, it’s part of Marvel’s multiplatform city-state. It faces a future of perpetual re-invention, and that puts it in the exhilarating first car of television’s roller-coaster ride toward possible world domination.

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‘Marvel’s Agents of S.H.I.E.L.D.’

Where: ABC

When: 8 p.m. Tuesday

Rating: TV-PG-LV (may be unsuitable for young children with advisories for coarse language and violence)