Josh Hartnett stars in "Fight or Flight." Asbury Park Productions/Sky UK via TNS

Balázs Glódi/Asbury Park Produ

Take note: if you have any anxiety about flying, James Madigan’s “Fight or Flight” will not be for you. But if a cheap and cheerful one-setting action thriller a la “Bullet Train” featuring one of the preeminent heartthrobs of the Y2K era is up your alley, well then belly up to this (airport) bar. This flick isn’t a masterpiece, not even a vulgar one, but it’s cheeky and entertaining enough in its giddy hyper-violence, thanks almost entirely to the star turn of Josh Hartnett, who has proven in his recent renaissance that he’s especially great in bozo mode.

Hartnett was the brooding bad boy in movies like “The Faculty” and “The Virgin Suicides,” which rocketed him to stardom in the late '90s. But in recent years, his career has been reinvigorated, playing characters like “Boy Sweat Dave” in Guy Ritchie’s “Wrath of Man,” and turning in an especially delicious double-time in M. Night Shyamalan’s “Trap.” In “Fight or Flight,” Hartnett looks straight out of the 2000s with his bleached hair and cargo shorts, the only difference is that he’s now unleashed, freed from those moody shackles; wild-eyed and frequently covered in fake blood the vibrant hue of strawberry jam.

Indeed, “Fight or Flight” wouldn’t work without his fizzy central performance that brings an edge of mania to the absurd premise, which is essentially “Assassins on a Plane.” The script is by Brooks McLaren and “Shazam” actor D.J. Cotrona, and it draws on the kind of “John Wick”-style story that that film perfected when it posed the question, what if there was a bounty on a hit man’s head? “Fight or Flight” borrows the conceit and sets it in a confined, high-altitude setting, taking a humorous tone for its action thrills.

Hartnett plays a down-on-his luck drifter named Lucas Reyes, who wakes up in Bangkok with a hangover, a black eye, and his hated ex Katherine Brunt (Katee Sackhoff), calling him for a favor. A high-level security professional, Lucas is her last option after a hacker known as Ghost has stolen billions in cryptocurrency following a terrorist attack. Katherine needs Lucas to get on the same plane in order to deliver the hacker into custody (alive), and he’s the only one she knows on the ground at the moment. When he boards the flight, he’s not aware that a bounty on Ghost’s head has spread across the dark web, and thus, the rest of the passengers are mostly assassins, looking to make an easy buck.

And so, aviation mayhem ensues, as Lucas fights off a coterie of bad guys through a haze of drugs and liquor. He has his own reasons for wanting to complete the task, events in his past that explain why he ended up on his journey to the heart of darkness through the bottom of a whiskey bottle in Southeast Asia. They are honorable, of course, and when we meet Ghost, we find out their motivations are similarly altruistic, if a bit shallowly written.

The filmmakers would rather focus on the outlandish violence anyway. Hartnett holds his own up and down the aisles, through the cargo hold, and into the bathroom, making use of the space and tools within his vicinity. But it’s more fun to watch his face move than his body, his crazed eyes and tight grins delivering the high-wire tension. He has great chemistry with a feisty flight attendant, Isha (Charithra Chandran), and faces every foe with a gritted-teeth intensity and a sense of genuine surprise whenever he bests one. Madigan is fond of the trick that is setting particularly bloody sequences to high-energy, tonally mismatched tunes — Hartnett bashes and stabs his way through everything from punk to polka aboard that flight.

But then the already goofy “Flight or Flight” takes a turn to the insanely cartoonish as it begins its descent, into a tangle of hallucinatory madness, unearned twists and mind-boggling cliffhangers. It’s a true Looney Tune with a shocking amount of digital blood, and almost squanders whatever appeal it may have churned up, except it all happens so fast. Surprisingly, Hartnett’s Lucas hasn’t worn out his welcome, even if the movie around him has fallen apart midair. Ergo, the old truism has never been truer: when it comes to “Fight or Flight,” your mileage may vary.

“Fight or Flight” is rated R for strong bloody violence, language throughout and some drug material. Running time: 102 minutes. 2 stars (out of 4).