“The Lost King” is a featherweight little charmer about a plucky Brit who decides that King Richard III, whom history and Shakespeare have rendered as a murderously psychotic, has gotten a bum rap.

As played by Sally Hawkins, Philippa Langley is woman entitled to that notion, an over 40 marketing exec, passed-over and dismissed at her Edinburgh firm thanks to ageism and perhaps ableism. She sees a ridiculed and reviled figure from the late 15th century as a kindred spirit.

Philippa has “ME,” myalgic encephalomyelitis, also labeled chronic fatigue syndrome. When she watches a production of “Richard III,” she sees someone with a disability whom Shakespeare made a villain simply because of his alleged appearance. His Richard was not just a homely heavy, but a self-aware one, “Cheated of feature by dissembling nature, Deformed, unfinish’d, sent before my time Into this breathing world.”

In Stephen Frears’ playful, fanciful film, Philippa becomes so obsessed with this possible victim of history that she starts seeing Richard — actually the actor (Harry Lloyd) she saw playing him on the stage — as a robed and crowned royal ghost tormenting her to find his long lost remains and perhaps clear his name.

The complications in a marketing exec undertaking such an undertaking about ancient undertaking — Richard was thought to have been tossed into the River Soar in Leicester, or perhaps buried somewhere else with no real record of it — begin with a skeptical ex-husband, played by producer and co-writer Steve Coogan.

Coogan re-assembles his “Philomena” team (which he also wrote for Frears) for this story, and turns his role into it into a lesson about exes who remain mutually supportive. John and Philippa get on well enough to raise their two sons, and when she starts skipping work and spiraling down the rabbit holes presented by joining the worldwide Richard III Society, he even pitches in to feed and house them all (he’s a construction site supervisor).

The film follows Philippa, whose connection to Richard Plantagenet grows so intense that she develops instincts and “feelings” about where he might be, through this “fan’s” first contacts with real experts. Veteran Brit twinkler James Fleet (“Sense & Sensibility,” “Four Weddings and a Funeral”) is Medievalist John Ashdown-Hill, who encouraged Langley, and had research all set up to verfiy her claim, should she find a candidate corpse.

Others are more dismissive, at least at first. Mark Addy plays a composite character from the University of Leicester, which wanted little to do with this hunt…until Langley secured funding to get their archeology department to dig where she just “knew” they’d find a skeleton with a busted skull and twisted spine.

The film sets up the U. and its hierarchy as villains, heirs to the Tudor propogandists who so smeared the last Plantagenet king’s name after vanquishing him and his army at Bosworth Field. Skepticism and “Why didn’t WE think to do that?” are one thing. If U. of L. indeed tried to steal the credit for her dogged legwork, direction, fundraising and instincts, they should be ashamed.

The consulting-with-a-ghost business sets the tone for “The Lost King” — curious, historical and whimsical. But the great Sally Hawkins makes us feel the weight of discrimination and injustice in a performance as fine and nuanced as any in her career.

Philippa’s physical pain does what such maladies always do in the movies. It comes and goes at the screenwriters’ convenience. But Hawkins never lets us forget that it’s there, this depressing limitation in life that plays havoc with her work, her marriage and her sadly circumscribed future.

“If I can find him, I can give him a voice,” she insists. And maybe give herself one, too.

We’re meant to be ever-so-furious when the university slickers steal TV time and credit for her project. And we bloody well are.

Coogan is effortlessly pleasant in support, Fleet, Addy stand out. And Amanda Abbington, as a city official who gives Philippa counsel about how to be taken seriously in the stuffy, dogmatic man’s world she’s invading, sparkles with a little keep-calm-and-stop-saying-“feeling” advice.

The film gives short shrift to the hunt itself. We see arguments at lectures, rowdy meetings of “Richardians” (Brits and their love for “royals”) and a little simple legwork that suggests intuition and a marketer’s hunch for how this “story” of discovery will be sold and told (she produced TV documentaries about the search, and is a producer here) were paramount.

A lot feels skipped-over and might have been better handled in a “this clue came from here” and “that one turned up there” methodical style.

When this story broke in 2012, much of the Shakespeare-speaking world was simply gobsmacked by the unlikeliness of it all. “The Lost King” gives the impression that Langley was born to do what no one else could be bothered to — narrow the choices to a spot, visiting it and get a “feeling,” and “Voila!” The movie makes that look too easy.

Then again, if the ghost of the dead, possibly murderous monarch is sort of pointing the way, it would be, wouldn’t it?

Rating: PG-13 for some strong language and brief suggestive references

Cast: Sally Hawkins, Steve Coogan, Harry Lloyd, Amanda Abbington and Mark Addy.

Credits: Directed by Stephen Frears, scripted by Steve Coogan and Jeff Pope, based on the book by Philip9a Langley. An IFC (Mar. 31) release.

Running time: 1:48