Friday’s “Send Help” strands a truly odd and very antagonistic couple on an anything but idyllic deserted South Pacific isle following a harrowing plane crash.

To say these two survivors – brainy but socially inept bookkeeper Linda Liddle (Rachel McAdams) and her arrogant, chauvinist pig of a boss Bradley Preston (Dylan O’Brien) – have “issues” is a massive understatement.

He’s super dismissive, she’s super capable.  If this is going to be a battle of the sexes, played against thunderstorms, a wild boar and risky mountain trails, Linda definitely has the advantage.

Directed by veteran horror helmer Sam Raimi (“The Evil Dead,” “Spider-Man”), “Send Help” rates as a true original, one that speeds along with continual, unexpected, hair-raising twists.

Is this, O’Brien, 34, was asked in a virtual interview, a satirical update of a feminist classic comedy like “9 to 5”? A rousing survival of the fittest adventure? Classic horror or a battle of the sexes that goes deep and dark?

“Hopefully,” he answered, “it’s indescribable. It’s all those things – and I love movies that you can’t quite pin down.

“Sam directs this tonal tightrope of an original film that has so many elements of horror and comedy it really feels like a wacky fun ride.

“And I understood the role I’d play.”

That means this is one couple insistent on continually revealing new facets, moods and surprises.

They may be at each other’s throats but filming on locations in Thailand and Sydney, Australia, was, unlike the sinister scenarios they were playing, a lot of fun.

It’s Raimi whom O’Brien credits with “allowing this thing to flourish in the way that we hope that it does.

“Rachel,” he discovered, “is as prepared as they come to set. She prepares in a way that is so thoughtful, so precise and practiced that it’s just interwoven into her DNA by the time we’re there each day and the cameras are going to roll.

“What that allows her to do is move in any direction possible. So I found that to be something very fun to play with. I think we both found that playful energy with each other because we genuinely just really enjoyed this job. Really enjoyed these characters. And the puzzle that it is.

“We were sort of calibrating each day these tonal shifts. These big swings back and forth, taking this audience on, hopefully, what would be like a really, really fun ride. One that, ideally, we earn. That’s a tall task but a really fun one.

“And,” he added, rubbing his trimmed beard, “when you have this camaraderie and genuine enjoyment of each other’s company, anchored by a fun sense of humor between the three of us – and the whole crew! – it just makes for a really fun time.

“Hopefully a lot of that magic shows up on screen.”

Rachal McAdams is Linda Liddle and Dylan O’brien is Bradley Preston “Send Help.” (Photo Brook Rushton/20th Century Studios)