Did you ever wonder how it’s possible to have secure communication in an age of near-total surveillance? Relay lays out a possible scenario, using details of a real-world service that “enable(s) people who are Deaf, Hard of Hearing, DeafBlind or those with a Speech Disability to place and receive phone calls.” In this movie, a same-named company uses the technology to oversee contact between those who don’t want their ugly secrets getting out, and whistleblowers who could expose them but would rather be paid off and sign a non-disclosure agreement. The process isn’t 100% secure. Nothing is. Relay is about a case where things don’t go as planned.

Riz Ahmed stars as Ash, a New York loner who works for Relay out of his small apartment and seems to have no friends or family. Lily James plays Sarah Grant, who works for a bioengineering company. Sarah’s employers have created a genetically manipulated grain that they advertise as a solution for farmers in impoverished countries. But it has toxic side effects. The company has decided to sell the grain anyway, and they’re about to get bought by another company for billions of dollars. The Securities and Exchange Commission filing is just days away.

Sarah’s predicament is laid out in an early scene when she seeks representation from a lawyer. She says she learned of the side effects of the grain and brought it the attention of higher-ups, but was ostracized, transferred, and finally harassed and stalked. She tells the lawyer she wants to sue the company for what they did to her. The lawyer tells Sarah, “I commend you for your intentions here, but we’re no longer interested in this kind of business,” then puts her in touch with Relay, which assigns Ash to handle her case.

What follows is an elaborate cat-and-mouse scenario. Ash handles the on-the-ground transfer of Sarah’s package of incriminating documents. Sarah, who has abandoned her old apartment and temporarily moved into new digs, communicates with Ash through Relay’s service. Meanwhile, a squad of goons paid by the corporation tries to figure out who the courier is. Throughout the process, the desk jockeys in cubicles at Relay’s New York office act as air traffic controllers, negotiating the movements of all parties and giving them very specific instructions that they must obey if the operation is to be successful for all involved. Large amounts of cash come into play at the beginning and end of the process. Relay gets an upfront fee for handling the secure communications (including Ash’s services), paid by both, Sarah and the company. The company is then expected to pay a much larger amount to Sarah once all of the details are wrapped up. She’ll sign an NDA, and the company must agree to abide by all the terms they agreed to, lest a “security” copy of the incriminating information be leaked to law enforcement and the media.

This is one of those cases where the plot of a film is clever enough that the reviewer would feel bad for including too many details, especially from the second half, which takes all the major players, who have mostly been moving the story forward by making calls via Relay and mailing overnight packages, and dumps them onto the street, where they run and drive around. Both sections of the story are well-done, but even though the first half has a few problems that become clear in retrospect, it’s more engaging than the second half because we’ve seen a lot of stories about smart but troubled young modern knights trying to help a beautiful damsel in distress evade predators in the city, but not one where the most important action is virtual.

Writer Justin Piasecki and director David MacKenzie (Hell or High Water) have clearly studied the classics of the so-called paranoid thriller genre. A lot of modern questions that viewers might have pondered while reading the news, like “how can a person remain anonymous in a world where everybody seems to know everything about everyone,” are answered here.

The technical aspects of the movie are superb, especially the wide-format cinematography and the sound design, which makes scenes with multiple speakers in different locations overlap each other in a realistic way, but without turning the dialogue track into mush. The movie’s relaxed confidence and eye for unusual details are commendable and could only have come from a creative team that put a lot of work into research and tried to integrate it into the plot in a dynamic way rather than dump it all out in expository monologues (although there are a few of those, mainly in the first section).

Sometimes a movie presents us with a character who is an enigma and keeps him an enigma (think of Clint Eastwood’s early roles), and other times it sets them up a question mark but then turns them into a full human being. The characterisation of Ash gets stranded between those poles. The movie might have been better off telling us less about him, because Ahmed is so watchable that he can get away with barely speaking during the film’s first half; and because each new detail we learn makes him less compelling. When you finally hear his explanation for why he does what he does, there’s no impact, because it’s what pretty much anyone would imagine.

Still, Ahmed once again proves himself a mesmerizing leading man. Most of Relay is carried by the actor’s introverted energy, which is contained and focused but can believably morph into impulsivity, obsession, and violence.