When calls start coming in to report debris on the M4 motorway, police discover that a father and son have been in a serious crash. As traffic chaos builds, the pressure's on for the collision team to find out why the car left the road.

When a Friday evening trip out in the car ends in a fatal crash, the driver refuses to accept his driving is to blame. The collision team must find the evidence to prove the real story of the night.

When a head-on crash leaves a grandfather dead, Chris discovers the answers could lie in electronic data within the car. As his mission to access it begins, he unearths an intriguing story of what really led up to the crash.