An incident on the bus on the way to work leads to Duffy clash with Mr Coulson, and ends with her quitting her job.
Actress Cathy Shipton has talked about her character's decision and teases where Duffy will go from here in an interview with Inside Soap.
"Duffy realises that her department is carrying a potential liability," she said. "Despite the fact she acted professionally, and Mr Coulson apologises, Duffy decides to call it a day.
"She doesn't want to end up making a choice that could be medically questionable."
She continued: "Hanging up her uniform doesn't mean Duffy is out of a job, though. They still want her involved in the ED, so another role is created for her."
Cathy doesn't completely agree with her character's decision, as she says that she thinks that Duffy could have moved into another area of nursing on a part time basis.
Duffy's storyline is one of the seven reasons why we at Digital Spy think that Casualty is absolutely on top form right now, and you can read our full list right here.
Casualty airs these scenes on Saturday (June 22) at 8.25pm on BBC One.
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