“How to Talk to Girls at Parties” is a candy-colored sci-fi confection set in 1977 London, where Enn (Alex Sharp), a shy Clash fan, meets and falls in love with a pretty member of a colony of visiting extraterrestrials.

The title notwithstanding, I hesitate to call this alien creature a “girl.” Although the character of Zan is played —or, in the parlance of the film, manifested —by Elle Fanning, her anatomical gender does not precisely conform to that of female humans. While Zan and Enn —short for Henry, pronounced with a Cockney accent —are mostly chaste, there are other scenes of interspecies sex, but it ain’t like in the movies (unless that movie happens to involve body-cavity probes).

Exactly what Zan’s colony wants here is unclear. Do they come in peace, e.g., for research? Or for more nefarious purposes? That question the central mystery of so many alien-invasion thrillers, takes a back seat to the enigmas of the human heart, in what amounts to a bittersweet, if slight, metaphor about love by John Cameron Mitchell (”Hedwig and the Angry Inch”).

The real question is this: Who exactly is more alien, Zan and her fellow E.T.s, who behave like androids dressed in haute couture, circa 1965, or Enn and his coterie of spike-haired and nose-thumbing punks (epitomized by the abrasive band manager Queen Boadicea, played by Nicole Kidman)? A girl, in the eyes of a teenage boy, is like something from another planet, and vice versa, or so the film suggests.

Although the movie is based on a 2006 short story by Neil Gaiman, it’s more like a version of “Men Are From Mars, Women Are From Venus,” with loud guitars. (There’s also an element of “Romeo and Juliet,” the central device of star-crossed love. That explains the climactic showdown between the punks and the otherworldly interlopers, which is tedious and far from the point of the film.)

Setting the film in the punk heyday underscores themes of personal freedom and defying authority. And there are heartwarming touches, despite a plot muddied by sci-fi mumbo-jumbo about cannibalism.

When it works, it works. And even when it doesn’t, it’s just endearing enough to earn forgiveness for its flaws. As Zan says to Enn, an aspiring artist and writer who shows her the comic-book zine that is his magnum opus: “There are contradictions in your metaphor, but I am moved by it.”