"Chain Reaction" is the 41st episode of Casualty and the premiere of the 4th series. It was preceded by "Caring" and followed by "Accidents Happen". The episode was directed by Andrew Morgan and written by Ginnie Hole.
A set of new staff arrive at Holby – a leather motorcyclist arrives in A&E, and unzips. It’s Alex Spencer, a new Student Nurse. Also arriving, new SHO Lucy Perry, registrar Andrew Bower – who is dating newly promoted Sister Duffy – and comic porter, Jimmy Powell, who is already getting into trouble – Charlie tells him off for not doing his work.
A woman, Barbara Hayden, is brought in with a heavy PV bleed. Lucy treats her and finds advanced signs of cervical cancer, Duffy is annoyed with her attitude, when she says it’s her fault for not getting it checked out earlier. Barbara’s two young children, Jessica and Brian, arrive to see her.
Two policeman, Tony and Nick, talk to a young hitchhiker, Jane, just before she gets a lift with a man. As she tries to resist his sexual advances, he crashes the car and Jane goes through the windscreen. This causes a pile up – where another car is spun over – in which the male driver dies – and a lorry carrying drums of chemicals crashes.
Nick persuades Tony to turn back to check on Jane, but come across the accident. As Tony goes to help the injured, he falls into a pool of hydrochloric acid and is severely burned. As his pregnant wife, Lorna, arrives to see him in A&E, he dies. Jimmy comforts his friend, Nick.
Cyril and Lucy go to the scene and treat the lorry driver, Len, by performing a chest drain. The mother comes to see runaway Jane in hospital, she has head injuries. The driver of the car she was in has a ruptured spleen.
Cyril has applied for a job in ITU and Charlie reveals Megan’s husband has left her after 25 years of marriage, and although Valerie has dumped her boyfriend Michael – she and Charlie aren’t together.