Thirty-eight-year-old Lesley is rushed in when her heart stops while she is driving to work, leaving Dr Morris battle to resuscitate her and investigate why a normally fit and well woman with no known medical problems would suffer such an attack. Abigail, aged 20, is treated for a painful neck injury caused by a riding fall, and 28-year-old Laura is brought in having a severe asthma attack. It is clear to Dr Fawcett she is deteriorating fast and that her heart could stop at any moment.