At first glance this looks like Mads Mikkelsen has done a Liam Neeson: traded character and nuance for a wild ride of a vengeance movie in which a beefed-up ex-military man seeks heavy justice for the death of his wife.

It’s not that at all, but the mixture of themes and tone is so unexpected that it takes some explaining. The set-up, obvious from the trailer, sees Markus (Mikkelsen) on a tour of duty in Afghanistan which, he explains to his wife, Emma, in a phone call and without offering much by way of regrets, has been extended by another three months. Later that day, Emma and daughter Mathilde are on a train when an explosion occurs, killing Emma, who took the seat offered to her by another passenger.

The passenger, Otto (Nikolaj Lie Kaas), is consumed with guilt but he is also a statistician who, with his genius hacker friend Lennart (Lars Brygmann), concludes that the combination of various factors made this an assassination and not an accident. One of the dead was a tattooed bikie about to give evidence against the Riders of Justice motorbike gang, while a man who suddenly got off the train was a possible but not definite facial recognition match to Palle Olesen, the brother of the president of Riders of Justice.

The vengeance plot unfolds full tilt with Markus as the alpha male who brings murderous muscle to this society of oddfellows, now joined by the overweight and phobic Emmenthaler (Nicolas Bro), who specialises in facial recognition and computers.

But an increasingly bizarre parallel subplot is all the while quietly derailing our expectations of a thriller movie about Markus turning vigilante. Markus, played with the intelligent restraint we have come to expect of Mikkelsen, is clearly suffering from PTSD, while Mathilde is trying to broach the distance between her and her father so they can grieve. When Mathilde catches the oddball trio of  Otto, Lennart and Emmanthaler plotting with Markus, they lie and pretend they are family counsellors there to help with the grieving and they do their best while revealing – on one occasion in a particularly shocking way – their own psychological damage. 

Riders of Justice starts as one thing and, while remaining that, becomes something else, an exceedingly dark yet sometimes very funny black comedy about mentally damaged people.

There is another strange strand as well that bookends the movie, involving a man with a white beard and his young niece looking for a bike for her for Christmas. When they find one, it is red and she has her heart set on blue. That triggers the theft of a blue bike, which happens to belong to Mathilde and which feeds into a chain of events that see her and her mother on the train. In this way it becomes a fable about the randomness of fate, how a chain of events can be casual rather than causal, and that even though the numbers never lie, they may not lead to the truth.

Purists may find the tonal mix off-putting but it can also be seen as an unpredictable and interesting piece of Danish cinema that follows Mikkelsen’s equally surprising and tonally diverse Another Round.