"Different Worlds - Part One" is the 543rd episode of Casualty and the first episode of the 21st series. It was preceded by "Get What You Deserve" and followed by "Different Worlds - Part Two". The episode was directed by Patrick Lau and written by Ann Marie Di Mambro. It's the first part of Casualty's 20th anniversary special.
The episode is split between scenes in the emergency department and scenes in Cambodia. In addition, it sees a guest appearance from Lisa "Duffy" Duffin, portrayed by Cathy Shipton, who was last seen in 2003.
Duffy has set up a clinic in Cambodia; "Duffy's Clinic", and Charlie, Guppy, Abs and Comfort head out there to help her out. Guppy and Abs are separated from the others, and decide to explore the town, where they meet a young boy named Chan who tries to befriend them.
In an attempt to impress them, Chan climbs a tree to gather coconuts for them. However, he ignores their warnings and soon falls down and Guppy concludes that he's got a subdural haematoma. Guppy's surgical skills are put to the test, without the aid of hi-tech medical equipment he is used to using back home. Guppy calls Harry to help assist him through the bur hole operation on Chan.
Charlie is having doubts about Duffy's current boyfriend, the clinic's surgeon, Mike, when he refuses to help in Chan's operation claiming to have had a glass of wine. Furthermore, he avoids answering questions about his life back in the UK, including where he trained and worked. When Charlie hints as his reservations about Mike to Duffy, she storms off and tells him she wished he'd never come.
Meanwhile, back in England, Maggie and Harry are learning to work with a new doctor on exchange from Cambodia, Somnang. A young man, Kevin, is brought in after taking an overdose. Despite promising him he will be okay, Harry is unable to give him his full attention as he deals with Guppy's call. When Kevin dies, Harry is upset he didn't do his best for him. When Somnang makes a flippant comment about the way death is treated back in Cambodia, Harry is angered and orders him out of his hospital.
An overweight man, Tommy, is brought in with sickness. Maggie learns he has had a gastric balloon fitted to try to lose weight to impress his neighbour, which has caused his current condition.
As tensions run high in Holby, things take a turn for the worse when a bus full of schoolchildren crashes and topples over.
- Main article: Different Worlds - Part One/Gallery.