You might allow an international espionage thriller a bit of leeway for being overdramatic at times, but this film doesn’t need any forgiveness. It’s based on the true story of Katharine Gun (Keira Knightley), a British intelligence analyst who leaked a top-secret memo about illegal U.S. government activity leading up to the Iraq war. Any film of this kind comes with story embellishments for dramatic effect, but in this case, they blend in and look like real life.

Knightley has perfected a set of expressions that convey believable emotion without the need for words. Every line in her face shows the fear Gun feels once the story blows up, and no scene seems contrived or overacted. The whistleblower has noble intentions, but she spends the entire film in torment over the dire consequences, and Knightley’s emotional range leaves no doubt about the character’s inner struggles.

For me, an experienced, talented cast is the top reason to buy a ticket for almost any movie, and this roster doesn’t disappoint. Knightley shares the screen with Ralph Fiennes, who plays a human rights lawyer defending Gun; Matt Smith, who portrays a London Observer reporter covering her story; and Jeremy Northam and Tamsin Greig, who appear in smaller roles. Adam Bakri plays Gun’s husband, Yasar, whose life is deeply affected by her decision.

Should you see it? Yes, it’s gripping and has a great cast. —J.J.