"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.
Cyril's keen to find out how his interview went but Charlieâ€˜s keeping quiet about it and Jimmy Powell is in trouble over his attitude to the job and Duffy clashes with the new doctor Lucy Perry, as Charlie shows her round. Duffy tries to help Barbara sort out her children but when she has to have an emergency operation, they are taken into care and her future's not looking good. She's taken to theatre and as she's been operated on, her children arrive and Megan goes to take care of them. Charlie tells Duffy that Megan's in a state of shock because her husband's left her and that why he's keeping her busy. Valerie shocks Charlie and Duffy by admitting they may have to go back to the department for the porters jobs, because of all of the complaints. Out patrolling in their police car, Tony and Nick worry about a young schoolgirl on her own, who refuses to return home and when they leave she gets a lift from a motorist. Template:Series 4