Tonight's (September 7) Casualty episode was the beginning of the end of Iain Dean's story and the show will be airing his swansong when it returns later this month.

Also coming up, Ethan's new story will gather momentum, while Mason continues to scheme and Rash's problems go from bad to worse.

Here is a full collection of the nine biggest stories you can look forward to when Casualty resumes on Saturday, September 21:

1. Iain reveals his exit plan

Fans will be saying goodbye to Iain Dean when Casualty returns later this month, but he still has a few small obstacles to climb before he departs.

Michael Stevenson is bowing out of his role as the popular paramedic after seven years, with Iain rightly taking centre stage in next Saturday's bittersweet episode.

After being inspired by the reappearance of his old friend Dixie tonight, Iain will follow through with his plan to join the ED team – but faces the tricky task of sharing the news with his crew mates Ruby and Jan.

2. Dixie's return stint comes to an end

Dixie's return stint will also come to an end next week, but not before she gives Iain some much-needed advice.

As we mentioned above, Iain's final episode won't be without its complications as his thoughts return to frequent flyer Mia's tragic fate last year.

With Iain already consumed with doubt over whether he's read to move onto pastures new, he's dealt another big blow when one a patients of his sadly passes away. Worried about her friend, Dixie tries to reach out to Iain afterwards but is irked when he insists he isn't ready to talk.

Never one to mince her words, Dixie wonders out loud if HEMS is the right place for Iain if he can’t process his emotions – leaving him with further doubts about his next step.

3. Iain leaves the ED

As Iain wrestles with his exit decision, he finds himself bonding with another patient called Anna, who had previously suffered a breakdown.

As Iain starts to chat to Anna, this inspires him to make a final decision over his future – but will he leave on a positive note? And what's next for him now?

4. Rash is left devastated over Gem

Rash is about to be dealt another devastating blow when he learns second hand that he's being dumped.

Rash's girlfriend Gem Dean headed out to Thailand to join him last month, but has since made the decision to stay out there more permanently.

Not knowing how to break the news herself, Gem will instruct Iain to break the bad news to Rash – who is understandably left heartbroken at the sudden breakdown of his relationship. What's worse is that Mason manages to overhear Rash's bad news and uses the situation to his advantage...

5. Mason makes an almighty mistake…

As Mason continues to prove that he's a force to be reckoned with, next week's episode will see him continue to defy order from Rash – with disastrous consequences.

With Rash distracted by being dumped by Gem, he joins an unsupervised Mason in relocating Hailey’s shoulder.

However, when it becomes clear that something has gone very wrong, Mason soon realises it was very much his mistake.

While checking over the x-rays, Mason realises that he showed Rash an outdated one – meaning the patient's arm was actually fractured, not dislocated, and they've just made it a whole lot worse...

6. …And throws Rash under the bus

(Not literally), With clinical lead Dylan understandably furious over the aforementioned blunder, Mason will continue to do himself no favours with fans when he pins the entire blunder on Rash.

Despite being acutely aware that he's very much to blame here, Mason uses his trump card by relaying some incriminating information he picked up earlier on – throwing Rash under the bus in the process. Shocker!

7. Ethan's story is revisited

Fear not, Ethan's new story hasn't been forgotten and be revisited again in next week's episode. When Ethan is called up to discuss Effie’s entrance onto the trial, he takes a big risk by outright lying to the Clinical Nurse Specialist about Effie's condition.

Effie is delighted when she later hears that she's got on the trial – but has Ethan crossed the line?

8. Will is suspicious

Next week's episode will hint that Ethan's feelings for his friend's daughter Effie could run deeper than friendship and it's not just fans who'll be picking up on it, either.

Will starts to question the relationship between Ethan and Effie after witnessing an affectionate moment between the pair, but is he onto something here? We've got a feeling he is.

With Rash already under immense pressure at work, he will find his problems going from bad to worse in the wake of Mason's mistake.

Still unsure over what really happened with the X-ray, Rash is forced to accept responsibility and is read the riot act from Dylan, and later Ethan.

Despite usually shying away from competition, Ethan has some particularly harsh words for Rash as he insists that he should be worried about his career because of what happened earlier. Can things get any worse for Rash?

Casualty airs these scenes on Saturday, September 21 on BBC One.