In the Yorkshire Dales, a car with 5 young soldiers onboard has crashed in the early hours, two passengers are trapped with one in a critical condition, possibly paralysed, and another with a broken neck, but the driver is unharmed.

At the scene, the victims are being rushed to hospital and the driver is under arrest after failing a roadside drink-drive test, although he states he swerved to avoid a deer in the road.

Despite drink-driving being the likely cause of the collision, Crash Investigator Paddy Green needs to establish if there are any other factors, including speed and mechanical defects, or was the driver telling the truth? A closer inspection of the damaged car raises another issue, Paddy suspects none of the backseat passengers were wearing seatbelts, While Paddy awaits the results of drug and alcohol tests, he returns to the scene to check for signs of animals and runs speed tests using hi-tech equipment.

In York, Police Control receive a call from the Ambulance service to attend a serious incident involving a pedestrian who's tragically lost her leg after being run over by a suspected hit and run driver.

As police officers arrive on scene, the driver returns and is quickly detained for questioning, but the man claims the pedestrian ran out into the road from behind a parked car leaving him no chance to avoid her.

While the driver is detained in police custody under arrest after failing a roadside drugs test, witnesses come forward to describe hearing a loud engine noise leading up to the crash.

Crash Investigator Nigel Varney is called in to investigate whether the driver is to blame or if the Pedestrian was distracted in some way when stepping out.  A dangerous driving charge against the suspect could hinge on CCTV footage from near accident and Nigel calls in Paddy Green to help calculate the driver's speed at the time of the collision.

After receiving a 999 call, North Yorkshire's officers respond to a serious car crash 20 miles north-east of York. At the scene, a middle-aged man is found thrown from an overturned car in a layby at the side of a busy country road on a dark winter's evening.

Paramedics and Police fight to save the casualty's life but tragically all attempts fail. With no witnesses to help work out how or why the driver crashed, Traffic Officers call in veteran Crash Investigator - Steve Kirkbright to establish the cause of the collision.

When Kirkbright arrives, hypotheses from the officers at the scene seem contrary to the evidence in front of him. Steve discovers the car was travelling in the opposite direction to what officers first thought, losing control and veering across the opposite lane on a bend without any signs of braking. The key question for Steve is why, and could the driver have been distracted or fallen asleep, or was anyone else involved?

While Steve returns to the scene in daylight to search for more clues as to how or why the crash occurred, Detective Constable Ed Drake is appointed as family liaison officer. Ed arranges to meet with the deceased's wife to provide her support and learn about his movements leading up to the collision.

Near York, PC Paddy Green and Traffic Officers respond to emergency calls reporting a serious crash on the A64. A stranded motorist has been hit from behind by a van driver moments after allegedly being seen reversing up the carriageway.

On arrival, Paramedics pronounce the stranded male motorist deceased and officers detain the shocked van driver for questioning.

Crash Investigator Paddy and the team begin gathering evidence and testimonies from witnesses to understand whether the van driver was culpable for the death. Should the van driver have seen the stranded car? Was he distracted in some way? Was the car driver reversing back up the carriageway as alleged by witnesses?  All key questions Paddy and investigating officers must answer during a lengthy crash investigation which could lead to the van driver facing a crown court trial and a possible prison sentence.