Joe looks and sounds and moves like he was plucked from a 13th century medieval battle and dropped into the 21st century.

He’s a thick, muscular, brooding presence with a wild thatch of hair atop his head and a bushy beard streaked with gray. His eyes are dark and menacing. More often than not, there’s blood on his hands — literally. When he takes off his shirt, we see his arms and back and torso are laced with nasty scars indicative of stories of pain and abuse we probably don’t want to hear.

Early on in Lynne Ramsay’s feverish and gripping and disturbing “You Were Never Really Here,” Joe gets to a pay phone in Cincinnati and makes a call.

“It’s done,” he says.

By this time we’re almost certain Joe is a killer, but we don’t know if he’s a hitman for the mob or a freelance gun for hire or some kind of unhinged maniac working with one or more partners. All we know for sure is, if Joe wants you dead, the odds are strongly stacked against you.

Joaquin Phoenix has never been shy about going big if the role called for it — and maybe even if the role didn’t necessarily call for it — but his performance here ranks as one of his best because of what happens between the outbursts.

When Joe is sitting rock-still in a diner and he can’t tune out the cacophony of everyday conversation rattling all around him, when Joe is flashing back to the abuse he suffered as a child and the wartime horrors he experienced, when Joe is awkwardly offering comfort to someone whose life he has just saved — Phoenix leaves a memorable imprint on each of these moments.

There’s a little bit of Jean Reno’s “The Professional” in Joe, and a little bit of Robert De Niro’s Travis Bickle from “Taxi Driver” as well. He is a killing machine and he is a tortured soul — but he’s a hero compared to the pimps and sex traffickers and pedophiles on the receiving end of his ball-peen hammer.

Joe lives in his boyhood home with his ailing mother (Judith Roberts), who nags him to meet someone and settle down, even though mom can see that’s probably never gonna happen. (“How’s Janice?” asks Mom. “Who’s Janice?” replies Joe. “You mean my girlfriend from 20 years ago?”)

When Joe isn’t taking care of Mom, placing a plastic bag over his head until he can hardly draw a breath or experiencing those terrible flashbacks, he’s on the job, i.e., killing anyone that stands in the way of him bringing home underage girls who have been kidnapped.

Alex Manette plays a wealthy, ambitious state senator who hires Joe to find his 13-year-old daughter, a runaway who has been taken by a ring of sex traffickers.

“I want you to hurt them,” says the senator.

This particular job takes Joe into places ever deeper and darker, with the cinematographer Tom Townend sometimes showing the action in effectively intense, changing points of view. Sometimes, we see Joe’s world from his point of view. In one extended and brutally intense sequence, security cameras capture a killing rampage.

Ekaterina Samsonov plays the senator’s daughter, who is in a near-catatonic state by the time Joe shows up. It is a role with little dialogue, but Samsonov is hauntingly good as a child who has had her childhood stolen in unimaginable ways — yet still finds a way to trust Joe, and has the incredible inner strength to tap into her own survival instincts.

“You Were Never Really Here” is filled with flashbacks and split-second visual detours and dark fantasy moments, right to the edge of overload and certainly to the point of creating confusion in the viewer’s mind as to what is real and what is not quite real. It has moments of pitch-black humor, as when two men are side-by-side on the floor, soaked in blood after a brutal battle with one another, and the excruciatingly terrible pop hit “I’ve Never Been to Me” plays on the radio — and the two men quietly sing along to it. OK.

There are moments of brutal bloodshed — but often we see the violence from a distance, or we see the aftermath of a vicious encounter. Nothing Joe sees or does in present life is as frightening to him as the demons of his past.

★★★1⁄2

Amazon Studios presents a film written and directed by Lynne Ramsay. Rated R (for strong violence, disturbing and grisly images, language, and brief nudity). Running time: 89 minutes. Opens Friday at local theaters.