It’s not the tried and true framework of romantic comedies that so many get wrong when they’re trying to film one. It’s the vital pieces of that frame — the characters, and who they hire to play them — and all the stuff nailed to that frame that let so many rom coms down.

“The Unicorn” doesn’t reinvent that which The Immortal Bard perfected 500 years ago. But this randy, comically cringe-worthy farce about two not-quite-committeds who test themselves by taking on a threesome, has engaging characters, witty performances and enough laugh-out-loud lines and situations to pay off.

It starts with “can’t quite commit” and climaxes with “the key to happiness.” That’s all you can hope for from any functioning romantic comedy, really.

Whatever Hollywood is imposing on the next upcoming Valentine’s Day as a “date comedy,” this indie comedy from the latest member of the Coppola clan to make movies almost certainly works better and plays warmer than LA assembly line product.

Lauren Lapkus of “Holmes and Watson” and TV’s “Big Bang Theory” and “Crashing” and Nicholas Rutherford (“Brigsby Bear,” TV’s “Dream Corp.”) play Mallory and Caleb. Shorten that to “Mal and Cal” and you get an idea of how connected these two simpatico smart-alecks are.

They’re SoCallers who’ve been engaged for four years, heading to Palm Springs for the weekend to see her mother (Beverly D’Angelo) and amorous stepdad (John Kapelos) renew their vows.

Mal’s sister Katie (Maya Kazan) and her husband (Darrell Britt-Gibson) are expecting twins. So there’s pressure — to be “as fun” as the parents, as together as the sibling.

“Weddings are fun,” Mom teases. “You should try one sometime.  A wedding, with invitations on stationary. And a date we stick to.”

But it’s learning that “they like to PARTY” (as in have the occasional threesome) is how the older folks keep it fresh is a bit daunting to nebbishy Cal and quirky Mal. It’s what sets them off.

“We’re like, a fun couple, right?”
“We’re FINE, right?”

Maybe they’re fine. And they’re kind of fun. Cal gives Mal a new “re-engagement” ring with his wisdom tooth mounted on it. Mal encourages little bar pick-up games (as Canadians) to rattle complete strangers and give themselves a laugh.

Then she meets drink-stealing wild-child Jesse (Lucy Hale of “Truth or Dare” and TV’s “Pretty Little Liars”) in cut-off shorts and an open blouse. And the vibe this “energy mixing” expert — “energyologist” — puts out is on the make and up for a little action.

“Does she WANT us? Is Everybody having a threesome BUT us?”

We can smell the sandalwood as Mal and Cal enter Jesse’s hippy den of sin. Her shadow screen striptease has them debating going through with this, carrying out hasty genital grooming and hunting for “safe words.”

“Wait — my CAR!”

So begins an almost-wild night in pursuit of “The Unicorn,” what they assume “EVERYbody” is doing (even the older folks), but is virgin territory for the pragmatic couple in the practical Honda Element.

There will confusion about who has what fantasy, revelations about things you’d think a couple engaged for four years and together for years longer, might have worked out.

They encounter Tyson (Beck Bennett of “Saturday Night Live”),  a gay strip club gay bouncer– or NOT gay…or Bi or…

“I feel sorry for people like you. So…limited.”

And there’s this gorgeous “massage therapist” (Dree Hemingway).

“Is she a prostitute?”

“Not a ‘tute!”

True confessions, titillating descriptions of their sex lives at home as threesome foreplay, an impromptu Uber evening (Cal’s job?) trolling for prospects and a lot of “Don’t fall for her/Don’t YOU fall for her” moments flesh out this evening long test of their love for one another.

And there’s just enough witty banter to put this over.

“Julia Roberts cost $3,000 a night!”

“Julia Roberts?”

“In ‘Pretty Woman.'”

“OK, we’re losing focus here…”

The trigger word launching barside every encounter?

“Shots!”

The leads are delightful together, perfectly believable as a couple and amusingly authentic as 30ish lovers desperate to be in on what the cool kids are up to.

Director Robert Schwartzman keeps the tone light and the pace between funny scenes and cringe-worthy moments quick. He’s the brother of actor/director Jason Schwartzman and son of Talia Shire and, with them and Sofia Coppola and Nicolas Cage, part of the extended family of Coppola filmmakers.

Schwartzman came up with the story here and had the good sense to get other writers (including co-star Rutherford) to liven things up and turn this script into, if not rom-com gold, at least rom-com silver.

MPAA Rating: unrated, sexual situations, drug jokes, alcohol consumption, profanity

Cast:  Lauren Lapkus, Nicholas Rutherford, Lucy Hale, Beck Bennett, Dree Hemingway, Kyle Mooney and Beverly D’Angelo

Credits: Directed by Robert Schwartzman, script by Nicholas Rutherford, Will Elliott and Kirk C. Johnson.  An Orchard release.

Running time: 1:29