Kempton Bunton (Jim Broadbent) is a man that’s impossible to hate, unless you happen to be married to him. As the central figure in the utterly charming new film The Duke, he has made a life’s work of sticking up for the little guy, no matter the consequences. He accuses his boss of discriminating against a Pakistani coworker and is sacked for his troubles. As a taxi driver, he lectures his fares about the plight of pensioners and gets fired. His crusade against the British government for requiring licenses to watch the BBC, which Kempton sees as a cruel tax on the poor, garners unwanted publicity for his family. His wife, Dorothy (Helen Mirren), is a private person seeking a quiet life, but she tolerates his escapades because she has no choice. Zealots don’t listen to reason.

It’s a role uniquely suited to the talents of Broadbent, who, if there were a dictionary of film archetypes, would be the first name listed under Charming Senior British Man. With his impish smile, polished head, and soft jowls, Broadbent is as unassuming as Mr. Magoo. His portrayal smooths over the rough edges of a character (based on a real person) who probably caused more suffering than he healed. In real life, we’ve all known people like Kempton, who put quixotic campaigns ahead of friends and family; in The Duke, he’s a harmless troublemaker whose unwinnable campaigns are portrayed as an eccentric hobby.  Even when we learn that Kempton has recently done a stretch of prison time, leaving his wife in a vulnerable spot and setting a poor example for his law-breaking sons, we shrug off his behavior with a laugh and a smile. That’s the effect Broadbent has on the viewer, making The Duke a winning marriage between character, subject, and star.

Directed by the late Roger Michell (who died after post-production last year), much of The Duke is framed as a lark, sort of an Ocean’s Eleven for the elderly. The split-screen camera work and jaunty score reassure the viewer that nothing too serious is going on here. But when Kempton steals a Goya portrait from the National Gallery, with plans to hold it for ransom and use the government’s money to buy television licenses for the poor, he threatens to push his family too far. He involves his son (Fionn Whitehead) in the deceit, and when Dorothy discovers his subterfuge, she threatens to leave him for good. The Duke follows in a long tradition of heist films that makes thievery seem like a ripping good time, but Mirren provides a counterbalance. Forgiving but unbowed in her frustration with Kempton’s obsessions, she shows us the cracks in his facade he refuses to see. Without her, The Duke would be an uncomplicated celebration of a knotty figure, but her grounded performance keeps the film from tipping into sanctimony.

Just when we are tempted to discover a rooting interest against the benevolent thief, however, Kempton turns himself into the authorities. Even then, a tragic ending hardly seems possible, but instead of drawing out the tension, the screenplay by Richard Bean and Clive Coleman, tilts towards the philosophical. His trial begins with a debate on the definition of theft—a loaded subject in 1961 Europe, when the stolen object is state-owned, and the value is to be distributed to the poor—but it begins to soar when Kempton himself is put on the stand to pontificate about his views on life. His lawyer (Matthew Goode) figures that, with a signed confession in hand, his only chance of getting his client off is to let him talk and hope the jury is as charmed by him as the rest of us.

Charmed, we are. There aren’t too many heist movies that hinge on a character earnestly declaring, “You are me, and I am you” to a crowd of people, but The Duke is unafraid to be romantic. It’s a film about the things that matter in life—love, sharing, forgiveness—or used to matter, anyway, before we all got old and selfish, and forgot about human decency. It will put a smile on your face, and while its conclusion might feel simplistic, The Duke never promised to tell the truth. It’s got higher aspirations than that.

The Duke opens in theaters everywhere on April 29.