"Step Right Up" is the 983rd episode of Casualty and the 22nd episode of the 30th series. It was preceded by "The Good Life" and followed by "Hearts and Flowers". The episode was directed by Jo Johnson and written by Rob Butler.
Ethan begins his shift after thinking about leaving the week before, and Cal tells him it's good to have him back. At the ambulance station, Big Mac hangs up a picture of Dixie to go with the one of Jeff. Him and Iain discuss the new replacement for Dixie when Rocker from HART enters and tells Iain that he will be Dixie's replacement whilst he's on a hiatus from HART. Meanwhile at a local fairground in Holby, a woman, Marie, is searching for her 16 year old autistic daughter Sash. Ron, Marie's father, is there with Sash and she asks him if her mum can come next time, and he ignores her and she realises it means no.
Back at the ED, Charlie notices Emilie come into the ED with her carer with an injury to her hand. He and Cal get her into cubicles whilst avoiding Ethan so they didn't encounter each other. When Cal asks her why she didn't go to her GP, she says she came to the ED to meet Ethan, whom she referred to by his birth name of Michael. After getting her into cubicles, Cal asks Charlie to keep Ethan out of his way and to get someone else to treat her. Back at the amusement park, Sash gets on a ride whilst Ron waits at the side, but Marie finds them and gets annoyed, causing Sash to get distressed. Ron goes through the barrier to try and get her out, but is pushed backwards by the ride when it begins and injures his arm. The paramedics arrive and Marie tells them that Sash fell down the stairs afterwards too, and they decide to bring them both into the ED.
Meanwhile, Charlie treats Emilie, but Robyn interrupts and brings Ethan in to treat her after she heard that a doctor was needed. Elsewhere, Marie, Sash and Ron arrive in the ED and although Sash says she wants her grandad, Marie tells him that he's not needed, clearly annoyed that he was spending time with her. Ron goes to get his arm checked out by Rita whilst Sash is being treated by Lily. Lily attempts to perform a scan but Sash becomes distressed and the results come out inconclusive, so she says she'll send her for a CT. Lily also notices Marie's cough, but she tells Lily that it's just the tail end of a cold.
Back in cubicles, Ethan continues to treat Emilie when Cal comes in shocked to see him there. Cal tells him that Lily needs him, in an attempt to get him away from Emilie. Ethan arrives to assist Lily but she already seems fine so he just stays to assist whilst Sash is brought up for a CT scan. Dylan and Rita treat Ron who says he wants to see Sash as he's worried. In reception, Robyn seems to be ignoring Lofty's instructions and Dylan tells him that he will need to assert some authority over her as he's in charge.
Elsewhere, Sash is going in for her CT scan. When Lily is unable to get her to lie down, Ron plays one of her favourite songs to get her to go in for the scan. In cubicles, Emilie attempts to get Cal to get Ethan back, but he says no. They discover she has a urinary tract infection and therefore have to keep her in for longer. She tells him that she didn't ask for any of it, but he lashes out and tells her that it's her fault for abandoning her kids, and Charlie defends Emilie. Back in observation, Lily notices that Sash has bruising on her stomach and that they want to keep her in for a bit longer. Ron is there to keep Sash calm, but Marie isn't happy to see him when she gets back, but she soon begins coughing again, and coughs up some blood into a tissue. Ethan and Lily check her out whilst Sash is moved to a new section for observation.
Just before Rita and Ethan order a chest x-ray to be done for Marie, she hands them a medical form which she says will save them time. Shortly after, Cal tells Ethan that he'd like to take him out for a drink after the shift but he says he's far too busy. Ethan then tells Lily that the form Marie handed them said she has lung cancer, and that they should try to get her to accept Ron's help as he clearly wants to spend time with Sash. In reception, Iain gets annoyed by Rocker when he starts flirting with Rita, and Jack clocks onto the two being in a relationship when he sees them talking. Elsewhere, Lily prepares to perform a chest drain on Marie after they discover a build up of fluid in her lungs. Ron comes in and she makes him promise not to see Sash anymore as he didn't look after her when she was young and she doesn't want him to do the same to Sash.
Ron goes to see Sash and when she asks him if she can go on the big wheel, Ron shouts at her and says he doesn't want to see her anymore, fulfilling Marie's wishes. This causes Sash to run away from him. Lily asks Ethan if he wants to go and see Sash with him as they have discovered a small internal bleed on her scan results, but they're interrupted by Robyn and Lofty asking them where Sash is. Ethan says he may have a clue where she is, and he gets a lift to the funfair with Big Mac, Ron, Iain and Rocker in the ambulance. Meanwhile, Emilie says she came to the ED to explain the truth to Cal. She explains to him that she felt like she was in a bubble watching her life and not being able to live it, and that she went to the doctor but she thinks he was the one who called social services. They came to her house and took Cal (then Stephen) and Ethan (then Michael) away, and she had to be held back.
At the funfair, the ambulance arrives and they find Sash atop the fenced of Ferris wheel, presumably having climbed up. Ethan volunteers to climb up and calm her down until rescue comes as if she's bleeding internally she could pass out at any time and fall. He climbs up narrowly avoiding slipping, and ends up sitting on the carriage behind Sash. He tries to calm her by singing her favourite song, but she stands up in the carriage and Ethan attempts to climb over to get to her. He almost falls, but to everyone's relief he gets across safely to Sash although his glasses fall off and break. Back at the ED, Charlie and Cal discuss how Emilie's mental state which caused Cal and Ethan to be taken away from her could have been down to early symptoms of Huntington's where patients find themselves with mental issues.
Sash arrives back at the ED, and although her bleed has worsened, Ethan says that the signs are looking good now she's back in care, and they will take her to theatre for a small procedure to stop her bleed. Marie eventually realises that Sash would be happy with Ron and lets him look after her. Outside the ED, Rocker gets off the phone to his boss at HART and has been told that someone has told him that Rocker isn't getting on in the ED. He suspects that it's Iain who reported him but lets is go and walks away ready to move on. Rita joins Iain in the ambulance shortly after and tells him that Rocker suspected that Iain had something to do with his removal. However, she's secretly glad to have him gone.
In the staff room, the staff gather to congratulate Ethan for his efforts during the day and managing to save Sash. Robyn is interrupted by Lofty who brings her outside to tell her that he's her senior now and she must do what he says instead of treating him as her equal. Lily and Ethan discuss the day which reminds Ethan that he forgot to go and check on Emilie, even though his shift is over. Cal tells Emilie that it wasn't her fault that she lost them as it was due to her illness and when Ethan walks in, Cal tells him that Emilie is their mum.
The reaction to this episode from fans was mixed. On social media, many people praised the fact that it was pointed out that all autistic people are affected differently, breaking the generic stereotype often present in other forms of entertainment. In addition, the BBC put up a special page on their official website after the episode for those affected by autism or Huntington's disease, two illnesses shown in the episode.