The poster for Snitch features Dwayne "The Rock" Johnson standing hugely beside a big truck. The look on his face suggests that somebody over the viewer's left shoulder has just parked a big poo on the former wrestler's front lawn.

All right! We know what we’re going to get here. It’s time to power down the frontal lobes and settle in for some extreme vengeance. If we’re really lucky, The Rock might hit somebody over the head with a stepladder.

Hang on a moment. What the heck is Oscar-winner Susan Sarandon doing in this? Oh Lord. It looks as if Snitch might actually be "about something important". You don't get Sarandon in a Rock movie unless that film has something to do with inner-city illiteracy, pollution of wetlands or some other issue I should pretend to care about.

Based on a true story, Ric Roman Waugh’s film has a beef with the US war on drugs. In particular, it objects to the draconian laws concerning possession with intent to supply. Mr Johnson stars as the father of a boy who, after merely agreeing to accept a suspicious package from a pal, finds himself facing 10 to 30 years in prison. The boy refuses to engage in a plea bargain that involves setting up any of his friends. So, dad decides to take on the drug lords (and the DEA) himself. He makes a deal with District Attorney Sarandon: if he can entrap a major supplier, his son will walk free with in a year.

To be fair, the set-up is well handled and the cast manoeuvre the furniture adroitly throughout. Some trucks do crash. Some firearms are discharged. But the plot is so grindingly linear and the narrative intricacies so poorly explained that Snitch ends up being a roaring bore of the most soporific stripe. Know your place, Dwayne.