Rachel McAdams takes her cutthroat comedy genius way beyond Regina George

“Send Help” — 3 stars

If you weren’t already a fan of Rachel McAdams, “Send Help” should convert you.

The actress is superb in the new horror-comedy from director Sam Raimi, which follows a pair of colleagues who survive a plane crash and become stranded on a remote island somewhere off the coast of Thailand. Numbers whiz Linda Liddle (McAdams) may have been too awkward and frumpy to command respect at her corporate job, but she thrives on the island thanks to years of obsessing over “Survivor.” She nurses her wounded boss Bradley Preston (Dylan O’Brien) back to health and, after the obnoxious man’s gratitude runs out, attempts to outwit him into submission while they await rescue.

McAdams has played cutthroat before, most memorably as queen bee Regina George in “Mean Girls.” But she is tasked with displaying it as a newfound trait when Linda finally cracks after years of being underestimated. The character struts around with an air of superiority as she builds shelter out of tropical trees and roasts freshly caught fish over an impressive fire, recognizing Bradley’s leg injury as confirmation that, for once, she holds all the power in their relationship. A devious glint appears in her eye when he compliments her survival skills to stay in her good graces.

“Send Help” marks McAdams’ first film role since her understated performance in the 2023 adaptation of Judy Blume’s “Are You There God? It’s Me, Margaret.” Her animated portrayal of Linda is a highlight of her impressive career, up there with her amusingly deadpan (and viral) line readings in the 2018 comedy “Game Night.” There are similar moments scattered throughout the Raimi film in which McAdams maintains her cool in circumstances so outrageous that you just have to marvel at her composure.

The actress finds a suitable partner in O’Brien, the onetime star of TV’s “Teen Wolf” and the Maze Runner film franchise, who proved his acting chops in last year’s twisted comedy “Twinless.” Bradley isn’t as complicated as Linda — he’s a spoiled rich kid who inherits a company and makes business decisions based on whether he’d play golf with you — but O’Brien’s natural charisma and exaggerated humor make his character a compelling figure in this marooned power struggle.

Raimi, known for directing the Evil Dead horror trilogy and the Tobey Maguire Spider-Man movies, carefully calibrates the tone of his film based on Damian Shannon and Mark Swift’s screenplay. He eases the audience into its body horror, starting with a scene in the office when Bradley stares in disgust at a bit of tuna salad stuck to the corner of Linda’s mouth. The camera zooms in and lingers on the white gunk, as though ogling it — a mild preview of the gross liquids and bodily substances to come.

And, boy, are there a lot of them. The plane crash is crazy violent, complete with visuals of Linda’s contemptible colleague (Xavier Smith) getting bloodied up as the wind whisks him out of the aircraft and smashes his head against its windows. There’s some vomit from Linda, Bradley and maybe even viewers, depending on how you fare during a super gory scene where Linda hunts a warthog for meat. That sequence, which takes place relatively early on, is among the best in a film full of laugh-out-loud moments.

The chuckles help keep “Send Help” feeling dynamic despite largely consisting of two actors in a single setting. The film peaks early; while its first and second acts are absolute riots, the third is shakier and builds to a finale more predictable than the rest of this story’s twists and turns.

But even if it doesn’t stick the landing — the plane didn’t, either — this journey is well worth undertaking. McAdams again proves she has real comedic chops that this island, and Raimi’s direction, have only sharpened.

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In theaters. Rated R for bloody violence and strong language. 113 minutes.