‘Only Living Boy': Good cast, bad story

It’s hard to know what to make of the protagonist of “The Only Living Boy in New York,” a dour but idealistic aspiring writer in his early 20s who, when he learns that his father is having an affair, embarks on his own ill-advised relationship with Dad’s 40-something mistress. Why on Earth would somebody do that? I mean, beside the fact that she’s Kate Beckinsale?

As explained by the mildly troubling, and more than mildly implausible, story by screenwriter Allan Loeb (“Collateral Beauty”), Thomas does what he does for two reasons. Partly, it’s to derail the affair between his father (Pierce Brosnan) and his lover, in thoughtful consideration of Thomas’s emotionally fragile mother (Cynthia Nixon). And partly, it’s a devious means to a dubious end: making Thomas appear more desirable to his true love, a sweet and age-appropriate young woman (Kiersey Clemons) who has, for the time being, relegated Thomas to the friend zone.

On the one hand, our hero is an immensely likable kid, thanks largely to the angsty charisma of Callum Turner (“Tramps” and “Green Room”) in the title role. The ethics-and-credulity-straining nature of his actions is mitigated by both his immaturity and his charm. What’s more, Thomas is egged on by a roguish authority figure, an older writer who lives in Thomas’s building, from which he leads the young man down the garden path, in a series of boozy man-to-man talks.

In the role of W.F. Gerald, Thomas’s perpetually potted neighbor/mentor - and the film’s narrator - Jeff Bridges tears into Loeb’s archly literate dialogue as if it were a plate of baby back ribs, pulling the tender words off the bone with his teeth and licking his lips with relish as he dispenses equal parts bad advice and liquor.

Let’s grant the movie leeway. Its rendering of cultured, neurotic Manhattan is spot on, if, at times, overly precious. Thomas’s father owns a successful publishing house; his artsy mother is depressive; and Thomas is fond of uttering such cynical bon mots as “New York’s most vibrant neighborhood at the moment is Philadelphia.” Yet the moral universe the film depicts is one of pure expediency. Gerald’s philosophy, for instance - and maybe the film’s, it’s not clear - seems to be that all misbehavior is permissible, as long as it’s potential fodder for art. The author’s magnum opus, for instance, is said to be a novel called “Fahrenheit 185” - the cooking temperature of heroin, we’re told - suggesting past addictions more serious than alcohol.

But as misguided as Thomas’s impulses may be, they’re nothing compared with the decisions Loeb ultimately makes. Round about the third act, “The Only Living Boy in New York” veers wildly off whatever course it had been on, leaving the realm of the improbable for the preposterous. Suddenly and without warning, it introduces a maudlin plot turn so far-fetched that it destroys all goodwill that the film and its appealing lead have so far managed to create.

The fault is certainly not in the film’s direction. Mark Webb (“500 Days of Summer”) brings the tale to the screen with as much authenticity as he can muster, and a real feel for the literary lifestyle, not to mention human imperfection. How ironic then, in a movie about wordsmithing, that “The Only Living Boy in New York” is tripped up not by tawdry behavior, but by terrible writing.