On a sweltering Friday afternoon in August, traffic is backed up on the M4 highway outside of London when a truck jackknifes across five lanes and causes miles of confusion and chaos. As the ambulances arrive, lives are changed and stories are unfolded. Barney Fraser is a harried groomsman trying to get his friend to the church. Mary Bristow is a widow hurrying to meet the dashing American soldier she turned down during the war. William Grainger is a charming young farmer who sees it all happen from his cow pasture. Jonathan Gilliatt is a star gynecologist trapped in the car with his mistress Abi, who is furious at being dumped. Emma King is the eager young doctor on call at the hospital when the crash occurs, and Patrick Connell and Georgia Linley are the truck driver and his hitchhiker on the way to an audition, the only ones who know what truly happened to make the truck spin out of control...