A sophisticated, topical thriller with an estimable cast sounds like a great way to finish off the summer movie season, so it's too bad "Closed Circuit" turns out to be such a tedious dud. Lacking the tension and sense of romance necessary to properly sell its tale of sparring lovers swept up in a shadowy conspiracy, the movie plays instead like a cut down BBC miniseries robbed of colorful character detail and slow-burn suspense.

Opening with a discreetly staged terrorist attack in London, the story quickly skips ahead to defense attorney Martin Rose (Eric Bana) preparing for the resulting trial of standoffish suspect Farroukh Erdogan (Denis Moschitto). Due to a quirk of the U.K. legal system, Martin won't have access to all the evidence. A Special Advocate has also been assigned to defend Farroukh in closed sessions dealing with classified government information.

The S.A. in this case also happens to be Martin's ex, Claudia Simmons-Howe (Rebecca Hall), who is not permitted to discuss the classified evidence with anyone -- including the accused and the defense attorney, who are also barred from attending the closed court sessions. Naturally, hiding evidence from the defendant raises some serious questions of how to properly balance civil rights and government secrets in the terrorism era, but "Closed Circuit" doesn't exactly have much to say about the very issues it brings into the mix. Instead, the goal is a '70s style conspiracy thriller where nothing is quite as it seems and corruption is systemic.

Despite accomplished pros in director John Crowley ("Boy A") and screenwriter Steven Knight ("Dirty Pretty Things," "Eastern Promises"), "Closed Circuit" feels weirdly pro forma. The twists and turns are ridiculously easy to predict -- some simply by virtue of how the supporting roles are cast -- and what little action there is arrives far too late in the modest 96-minute running time. At its strongest, the film generates some excitement by cutting between Martin and Claudia's separate investigations, but the script keeps forcing them back together in a misguided attempt to personalize the wall between the defense and the Special Advocate. They're at risk every time they communicate, but we rarely feel the danger.

It might work if Bana and Hall displayed any kind of natural chemistry together, or were permitted scenes and dialogue to flesh out their bland characters' romantic past. Instead we're simply meant to take for granted they have a bond that transcends, and eventually overtakes, their court-appointed roles.

While Bana and Hall are stuck carrying the show in thankless lead roles, the supporting players are allowed flashier -- if no better developed -- turns, including Ciaran Hinds as Martin's longtime colleague, Jim Broadbent as the shady Attorney General, Riz Ahmed as a MI5 agent offering unwelcome assistance to Claudia, Kenneth Cranham as the judge on the case, Anne-Marie Duff as an unusual government employee and Julia Stiles as an American investigative journalist.

The recent box office success of "Lee Daniels' The Butler" and Woody Allen's "Blue Jasmine" proves there's an audience hungry for grown-up entertainment in wide release. They won't find any nourishment here. If anything, "Closed Circuit" stumbles by trying too hard to cater to "mature" viewers: It's exceedingly polite and seemingly afraid to do anything that may make audiences uncomfortable. That's exactly what you don't want from a thriller.