Directed by Fernando Leon de Aranoa

Written by Fernando Leon de Aranoa and Diego Farias, based on a novel by Paula Farias

106 minutes, rated M

Modern movies do not walk. They run at a pace that editors and directors never dreamed possible 20 years ago. Good editing used to be timed around the human heartbeat; modern action is more like the moments before a heart attack.

Older people find these new films for youth hard to watch – and vice versa. That’s why a film like The Wages of Fear (1957), one of the greatest thrillers ever made, might strike modern kids as slow. If they were remaking it now, Yves Montand would not drive a beaten-up old truck full of nitroglycerine; he’d steal a super truck like the one in the latest Mad Max and be chased by drones or dragons or zombies.

A Perfect Day is the first English-language feature of a Spanish director who has made five features: four of them won major Spanish awards. A Perfect Day premiered at Cannes last year to muted praise. A bit slow, said the trades, if well done.

That’s true but deceptive. The slow pace makes it work. Slow is not the same as dull. The film covers a full 24 hours, so the passing of time is important.  It’s trying to reflect the daily reality for international aid workers in a war zone.

We are somewhere in the Balkans, 1995. Dry and mountainous. We follow two teams from ‘Aid across Borders’ in their 4WD vehicles. The war is over, but bands of soldiers are still killing civilians and booby-trapping dead cows on the dirt roads.

Tim Robbins in headband drives one truck, with new girl Sophie (Melanie Thierry). He’s known simply as ‘B’ and he’s a little zen, a little crazy. He drives straight over the cow rather than risk the mines off to the side.  Benicio del Toro drives the other. As head of security, Mambru has seen it all. He has one more week to go. The interpreter Damir (Fedja Stukan) prefers travelling with him. B never shuts up, Mambru rarely speaks.

Their immediate problem is a body in a well. Someone has dumped a fat dead man there to contaminate the water. Trying to drag it out, their rope breaks. You would not believe how hard it is to find a new rope. A ten-year-old boy, Nikola (Eldar Residovic) offers to help, if they take him to his house.

The first scenes are black comedy. That gets muscled aside by a growing unease and tension, as we learn about the situation in which these people work. They are trying to do good things in a place where bad has been in charge. It would be easy to end up dead.

It’s based on a novel by a Spanish doctor, Paula Farias, who has worked all over the world in Medicins Sans Frontieres. It’s the kind of film that might once have starred Humphrey Bogart and Lauren Bacall – flinty, sharp dialogue, understated romance, gripping setting. Del Toro wears his role like a beaten-up glove, his voice as dry as gravel, and Robbins is funnier than he’s been in a while.

Olga Kurylenko complicates the picture, as a colleague who had an affair with Mambru, an under-developed role. It’s odd that a film based on a book by a woman has an old-fashioned kind of sexism in which women only cause trouble, but I have not read the book. What the film does well is to immerse us in the tragic weirdness of wartime logic, where nothing works as we would expect. It’s a strong, engaging film about how hard it is to wage peace.