Johnny Mad Dog (Christopher Minie) is a 15-year-old boy from an unnamed African country whose village is assailed by rebels.

After they force him to shoot his father, they induct him into a squad of feral young soldiers, armed to the teeth and instructed to rob, rape and kill until those who support the government give up the battle.

Writer-director Jean-Stéphane Sauvaire's film is not an easy watch.

But it drums home the lesson that anybody can be made to do anything once their mind has been beaten to pulp.

The film's second major character is Laokole (Daisy Victoria Vandy), a 16-year-old student in the capital who is trying to care for her disabled father and small brother.

When she meets Mad Dog, she accuses him of being a murderer - he excuses himself in the name of patriotism. No romance is implied but perhaps he sees in her some of the decency he has lost.

Mostly, however, we see the way the boy soldiers, all taken by force, are encouraged to behave like animals as the civil war progresses.

Shot in Liberia - where the election of Ellen Johnson Sirleaf in 2005 only made filming possible after 15 years of bitter conflict - the film has an immediate power no one could deny.

Many of its cast are former boy soldiers who fought for the now arraigned Liberian warlord Charles Taylor. Sauvaire says he approached the film as therapy for them.

Whether you believe that or not, Johnny Mad Dog shows very clearly how ritual, costumes, nicknames, drugs and guns can prevent young people being themselves and turn them into a group killing machine.

You can't help thinking of London gangs, fortunately not yet possessed of Uzis and mortars.

In that way the film - only squeamish because it knows even worse things happened than are shown - becomes an awful warning.