You may not have heard of “Closed Circuit” unless you’ve been paying close attention.

Its Labor Day Weekend release date does not bode well for the movie because this is routinely a time for movies to be “dumped” on the big screen as an indication that they’re not among the Oscar-worthy films of late fall, nor are they one of the summer blockbusters.

“Closed Circuit” is an enjoyable, rather quiet British thriller with no pyrotechnics or superheroes. Instead, it’s more of a courtroom drama about politics and cover-ups.

It’s no secret that surveillance cameras abound in London, where the story opens on a busy street. We see groups of various people, all busy talking on their cellphones, visiting or shopping until their world literally explodes. We then learn that 120 people have been killed in a suspected suicide bombing.

The suspect is identified as the leader of a terrorist cell named Farroukh Erdogan (Denis Moschitto), who is to stand trial for mass murder. Erdogan is represented by two attorneys: Martin Rose (Eric Bana), who will be at Erdogan’s side in court, and Claudia Simmons-Howe (Rebecca Hall, “The Town”), who will represent Erdogan in closed court.

Unlike Martin, Claudia will be able to see sensitive and otherwise-unavailable material that could compromise the country’s security. Making matters even more complex is the relationship, or rather, the former relationship, between Martin and Claudia. They once were lovers, but now they bristle at the sight of each other.

As the investigation into the bombings continues, both Martin and Claudia begin to realize that they, too, are under some kind of surveillance. And Martin’s supervisor (Ciaran Hinds) and the attorney general (Jim Broadbent) have threatening conversations with him.

This is one of those thrillers that demands you pay attention while clues are revealed every few moments.

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Bana and Hall are enjoyable and adept, as are the more minor characters played by Hinds and Broadbent. This is a talented cast whose performances rely mostly on dialogue rather than situations for their character development.

The movie is subdued in every way, even as characters begin to, sometimes literally, run for their lives. Yes, there are a couple of action sequences, but they are nothing like the CGI-stoked scenes in so many films that preceded this show on the big screen this year. This is more suited for the audience of the espionage tale “Tinker Sailor Soldier Spy” from a couple of years ago.

It’s a solid political mystery that’s worth your time, even if may not be worth an Oscar nod.