At Reading Services on the M4, 72-year-old retired college lecturer Steve steps out of his car and suffers a cardiac arrest. Dr Laura Douglas Beveridge and critical care paramedic Hannah Hirst rush to the scene. Elsewhere, a car rolls down a motorway verge, leaving both the driver and passenger critically injured. Critical care paramedic Barry Walsh and Dr Henry Knott are despatched.

A 999 call comes in reporting a car has hit a group of pedestrians - paramedics Mark Hodkinson and Adam Panter are immediately dispatched. Dr Tim Wait and paramedic Matt Hale come to the aid of 61-year-old Robin, who has fallen and broken his leg. Also, the medical skills of Dr Suzy Stokes and paramedic Joe Epton are required when 75-year-old Jacqueline collapses and suffers a cardiac arrest.