This argentinian film won the 2009 Oscar for best foreign film. I suspect it triumphed because not only is it moving, beautifully made and delightfully unpredictable, it is also not an "art film". Rather, it is an old-fashioned popular movie designed to entertain, and it gave me the most satisfying two hours I have spent in the cinema for a long time.

It begins in contemporary Buenos Aires with Benjamin (Ricardo Darin), a retired criminal investigator working on an autobiographical novel that revisits the 25-year-old murder case that changed his life. His research brings him back into contact with other unresolved matters, including the beautiful young colleague he loved at the time.

In flashback you see him in 1974, then a cynical investigator for a Buenos Aires judge. The only things that hold his interest in the paper-strewn office are banter with his number two, Sandoval, and his moments with Irene (Soledad Villamil), the judge's beautiful, upper-class assistant who seems to enjoy his company despite the unbridgeable social gulf between them.

One day Benjamin is called out to a murder scene. The victim is a lovely young woman and something about her - and her devoted husband - touches him. So when a colleague "closes" the case by having the police force a confession from innocent men, Benjamin insists on continuing the investigation. It gets him into trouble with his bosses and with the dark forces in Argentina about to take power in the 1976 military coup.

The Secret in Their Eyes does not conform to normal genre rules. It is more like an epic Latin American novel - except that it does not indulge itself in magic or political rants. It is part romance, part murder mystery, part political thriller. There are moments of comedy, of melancholy, of suspense, joy and dread. With remarkable daring it shifts tone again and again, but in a way that is not at all distracting.

The director Juan Jose Campanella has worked extensively in American television (on programmes like Law and Order) as well as in Argentina. And except for one extraordinary shot that sweeps down from above a football stadium into the stands, there is no self-conscious virtuosity, just skilled, exhilarating storytelling.

At one point a character looking back to the traumatic events of 25 years before wonders if his memories are accurate or if they are memories of memories. It prompts you to wonder how much of what you are seeing is what really happened or rather what Benjamin wishes had happened. It gradually becomes clear that among the film's underlying themes is that of the powerful human desire to see things resolved or fixed, like in a novel.

But as one character wisely tries to impress on Benjamin, you can pay a terrible price for spending too much time looking back - "you'll have a thousand pasts and no future".

What makes it all work so well are the superb performances, in particular those by Ricardo Darin and Guillermo Francella who plays Sandoval, Benjamin's clever, doomed alcoholic assistant, the Sancho Panza to his Quixote.

It is not a perfect film. There is something a little rushed about the final scene and occasionally it flirts with the kitschy melodrama of Latin American telenovela soap operas. However, it is engrossing in a way that movies almost never are these days. It feels like a film like they used to make them.