This is a prime example of what I like to call a Quality Awful Film.

“The Age of Adaline” has grand ambitions to become a timeless romance – a serious-movie score, an omniscient narrator who speaks as if he’s gifting us with every page-turning piece of information he doles out, beautiful costumes and sets and scenery, and quite the cast, from always-welcome veterans Harrison Ford and Ellen Burstyn to Blake Lively, who has the look of an old-fashioned movie star and a genuinely winning screen presence.

’Tis a pity they’re mired in a stunningly wrong-footed journey that begins with an attempt at bittersweet magic and ends on a series of sour and increasingly dopey notes.

This is one of those movies that have you wondering: Long before the actors signed up and the locations were chosen and the sets were built and the filming began, how did someone not say, “Um, we have a big problem with this story”?

Lively spent a half-dozen seasons on “Gossip Girl” and has carved out a decent career as a film actress, shining in supporting roles in films such as “The Private Lives of Pippa Lee,” “The Town” and “Savages.” She’s front and center and onscreen nearly every minute in “The Age of Adaline,” and though the performance is fine, she’s stuck playing a mopey, often-selfish character who treats her superpower as if she’s been cursed.

Here’s the deal. Around 1930, when Lively’s Adaline Bowman was a beautiful widow in her late 20s living in San Francisco with a young daughter, she was in a bizarre one-car accident involving shifting tides and lightning strikes and a fancy scientific phenomenon that won’t officially be discovered until the year 2030, as Ultra Serious Narrator Man (Hugh Ross) explains. The result: Adaline not only survives, she literally becomes ageless. She’s stuck at 29 forever.

Peter Parker and the radioactive spider make for a more plausible origin story.

But this is no superhero movie. Adaline is understandably freaked out by her eternal youth (one imagines it must have taken at least a half-dozen years before she figured out she wasn’t aging at all), but rather than go public or seek medical attention, she lives in the shadows – constantly changing her name and avoiding contact with longtime friends and associates who might happen upon her as middle-aged persons in, say, the 1950s, and say, “What the heck, Adaline?”

Only Adaline’s daughter, Flemming, knows what’s what. Flemming is played by Cate Richardson as a young woman, and by the great Ellen Burstyn when we pick up the story in modern times. Even though the 80ish Flemming calls Adaline “Mom,” it never feels for a second as if she’s anything but Adaline’s mom, or grandmother.

Then there’s the matter of the dogs. Adaline had a dog as a young woman, and over the years she’s outlived her dog, her dog’s dog, her dog’s dog’s dog, etc. Whenever one of the dogs dies, Adaline adds his photo to her scrapbook of all the dogs she’s loved before. That’s kinda creepy, Adaline.

But wait, there’s more. Adaline’s best friend is blind. Good move! That way, the best friend never says, “How much plastic surgery have you had, girl?”

One can sort of understand why Adaline changes identities and locales every 10 years. She doesn’t want to become “a specimen,” as one character who knows her secret puts it. On the other hand, seeing as how Adaline not only looks 29 at the age of 107, but is seemingly immune to illness, organ breakdown or, for that matter, any health problem, wouldn’t it occur to her to share her miracle with the world in the hopes it could lead to medical breakthroughs?

Also, whenever Adaline gets too close to anyone, she simply disappears. Mean.

Finally, after 80 years of running and denying herself true love, Adaline gives in when she meets a handsome, wealthy, annoyingly noble do-gooder named Ellis (Michiel Huisman from “Game of Thrones”), who instantly falls in love with her.

Which brings us to the plot twist where “The Age of Adaline” plummets from mildly interesting mystical romance to ridiculous, cringe-inducing, laughable and really heavy on the “ICK!” factor. Harrison Ford shows up as a crusty retired astronomer, and all I’ll say is he has a connection to Adaline that kills the movie. Even in a fairy tale, when you paint yourself into a corner, you paint yourself into a corner. Just when we should be reaching for the handkerchiefs and rooting for old-fashioned romance to triumph, “The Age of Adaline” creates a situation that’s just ... gross.

Lively looks great in modern garb and period-piece costumes. We can understand how a man could fall in love with her on New Year’s Eve by locking eyes with her across a crowded room. Ford livens things up with a hammy performance, which is so much more interesting than when he falls back on one-note stoicism. San Francisco looks gorgeous and a little bit noir-ish, befitting the tone of the film.

Or should I say the tone the film was hoping to achieve. Rated PG-13.