On a warm evening in a French seaside town, casually dressed pedestrians throng the length of an elegant promenade, filling its restaurants and bars. Suddenly, an ambulance speeds down the road, its siren cutting through the chatter. The rear doors are flung open and a white object is thrown into the street. It's the corpse of a doctor, who's been stabbed. The occupants of the ambulance then start shooting at the crowd, before hurtling at top speed into a group of people sheltering at a bus stop.