On his hundredth birthday, Allan Karlsson (Robert Gustafsson) decides he has had enough of life in an old folks' home and gives the staff the slip. Wandering to the nearest bus station, he is preparing to get the next bus out of town when a thuggish skinhead asks him to keep an eye on his hefty suitcase. The skinhead goes to the toilet, a bus pulls up, and Allan climbs aboard, still clutching the case, and heads off to the middle of nowhere. The case is – of course – full of money belonging to a psychotic gangster, and this shaggy dog tale is only just getting warmed up.

Allan narrates the story in laid-back, reflective tones, prompting frequent flashbacks as he fills us in on his remarkable, ridiculous life. Obsessed with explosives from a young age, he tells how his skills brought him into the employment of dictators and presidents – Franco, Stalin and Reagan all appear – while all Allan ever really wanted was a decent shot of vodka.

This might all sound like a Swedish Forrest Gump with an OAP twist, but that would be to miss the crucial detail: this is a blacker than black comedy. Unassuming Allan leaves corpses in his wake with every step, from exploding generals to deep-frozen white supremacists to elephant-crushed crooks.

It is material that could come off as crass – knockabout comedy in the Russian Gulag, anyone? – which is exactly the problem with the bestselling book the film is based on. But this is a rare incidence of a film adaptation that is much more successful than its source, as director Felix Herngren gets the balance of callously dark humour and playful, silly storytelling just right.

Reviewed at Glasgow Film Festival 2014.