An ambulance screams through London's streets, siren wailing, lights flashing. Inside, a paramedic tries desperately to save a man's life, with his distraught fiancEe by his side. Suddenly, the ambulance is rocked – a car swings across, a sickening crunch of metal, sparks fly. The ambulance is forced off the road, flips and rolls, finally crashing on its side, lights still flashing, siren still screaming.