Every thriller needs a good hook, and “Relay” has a doozy.

How can you protect your anonymity and preserve your identity in the modern surveillance state, when data harvesting, phone bugging and tracing has moved from the state into the private sector? How do you keep thugs of a corporate, criminal or governmental nature in the dark when there’s money and dangerous secrets you’re dealing with?

Our hero here has figured out the rules, tricks and arcane blind spots in the procedures of dying U.S. Postal service.

And he doesn’t just stop at a succession of burner phones when talking with people who would love to do him professional, personal or physical harm. He’s gained access to “relay” services for the hearing impaired. He can call in, have them complete the call — and then he types his side of the conversation with a corporate whistleblowers or the folks who want those whistles unblown. Nobody involved ever hears him, much less knows who he is and where he might be. That’s privileged communication.

So kudos for screenwriter Justin Piasecki, who gets his first produced script on the screen for coming up with this grand gimmick. And further congratulations for landing Riz Ahmed as his star, a sort of fixer, a non-violent “Equalizer” who stops intimidation and threats by people who hire heavies to keep their deadly secrets for them.

For much of the film, Ahmed’s unnamed (until the third act) fixer doesn’t speak. He communicates to those seeking his service via his Ameriphone dialogue phone, and for a long while we wonder if he’s playing another man with hearing loss after his powerhouse turn in “Sound of Metal.”

But no, this unnamed functionary is just very, very cautious. We see him communicate to a client (Matthew Maher), giving him precise instructions about how to hand off documents and a payoff from a corporate wrongdoer (Vincent Garber) in the opening scene.

A cute touch. They have to take a selfie together to seal the deal and ensure the threats will stop.

Our intermediary goes to great extremes ensuring his client safely makes his getaway. It’s implied that he probably provides his services to genuine do-gooders who expose those who endanger the public health by speaking out. But our “hero” isn’t a crusader. He’s a specialist getting paid by those whistleblowers needing protection, and money extorted from the wrongdoers they’re agreeing to not expose.

He’s anonymous to all involved, just a phone number with voice mail some lawyers have in case a client needs that kind of help.

Lily James is Sarah, a corporate scientist who saw an email pointing to cancer concerns in a new “fertile crescent” wheat varietal she worked on. She just wants the “harassment” to stop. She’ll hand over whatever documents she has if her former employer will “just leave me alone.”

Her car was set on fire. A quartet of corporate goons (Sam Worthington, Willa Fitzgerald, Pun Bandhu and Jared Abrahamson) are brazenly stalking her and staking out her apartment.

Sarah’s worries start to ease as she’s sent new phones, carefully detailed instructions and places to ship her documents and cash via these relay calls.

“Do not contact them yourself,” she’s told. “Do not respond if they contact you.”

He will do the talking, via text. He will threaten them with exposure, a bit of leverage that has lost much of its sting in our lawless, paranoid age.

The early acts in this David Mackenzie film — he did the terrific “Hell or High Water” — crackle with intensity and the quiet competence of a character who knows his tradecraft. Our “Equalizer” is always a step or two ahead of the bad guys, wearing disguises, sending Sarah traipsing through airports to sniff out who’s pursuing her and throwing them off the scent.

Even the more melodramatic turns in the story have a logic to them that works its way into the latter acts as we learn the guy’s name is “Ash,” that he’s in AA, that he’s smitten by the good-looking scientist who sees him as her savior and who wonders if he’s “lonely.”

And Ahmed, poker-faced start to finish, puts us in this guy’s shoes and in his head when his best laid plans are derailed, his “control” is shattered and his identity endangered. It’s another great character turn by a star who’s gained his leading man status the old fashioned way — by giving one raw, layered and compelling performance at a time.

Rating: R, violence, profanity

Cast: Riz Ahmed, Lily James, Sam Worthington, Will Fitzgerald, Jared Abrahamson, Eisa Davis, Matthew Maher and Victor Garber

Credits: Directed by David Mackenzie, scripted by Justin Piasecki. A Bleecker Street release.

Running time: 1:52