Officers are called out to a number of serious crashes, including a collision between three cars on a busy Derbyshire road, leaving one of the vehicles on its side on top of a van. A lorry driver hits a barrier on a bridge, causing his vehicle to jack-knife with his front wheels and cabin hanging over the edge, and the cops also race to a bus whose driver has swerved off the road into a field, with 20 passengers inside. But as they investigate, there is another collision between an ambulance and a police car