"History Repeating" is the 1000th episode of Casualty and the 39th episode of the 30th series. It was preceded by "You Make Me Sick" and followed by "What Lies Beneath". The episode was directed by Sean Glynn and written by Rebecca Wojciechowski.
Series producer Erika Hossington revealed in an interview conducted by Digital Spy in 2015 that the 1000th episode would be special, as it would only be set in the hospital. She also revealed that an old face would reappear. In June 2016, it was announced that Cathy Shipton would reprise her role as Lisa "Duffy" Duffin for the 1000th episode before returning as a regular cast member again at the start of series 31.
Hazel arrives in the ED with Rihanna, much to Dylan's annoyance. She requests to have Dylan treat Rihanna but he asks Robyn to get Ethan to treat her. Robyn also speaks with another pregnant woman, Soph, who's waiting to be seen for her painful arm. However, she soon leaves upon deciding that her case doesn't constitute an emergency, although Robyn advises her to stay. Meanwhile Elle arrives in the ED with her head held high but she still continues to get the cold shoulder from the rest of the staff. She sees Charlie outside the ED and welcomes him back and she tells him that she's been getting a negative reception from the rest of the nursing team. Charlie explains to her how his team operate on trust, before walking away. Noel struggles with the task of clearing out Big Mac's locker.
Elsewhere in the ED, Ethan treats Rihanna and asks Hazel if she's been around any smoke at all. Hazel says that she hasn't as Brian quit after being diagnosed with COPD, although Dylan overhears and doubts it. Louise and Robyn purposely give Elle the task of dealing with a diabetic person's foot ulcer in an attempt to lumber the worst patients on her. Elle also asks where Soph has gone and Robyn tells Elle that she left. She goes looking for her outside and eventually finds her and persuades her to come back in for treatment to check everything's okay.
Dylan takes over in treating Rihanna and decides to run some further tests. At the ambulance station, Iain admits to Jez that he has break-up sex with Rita the night before. She arrives at the ambulance station looking for him and as Iain goes to quickly leave with Jez, he injures his genitalia on some nearby equipment and is admitted into the ED. Meanwhile Elle reads through Soph's notes and discovers she had previously had a c-section which resulted in a stillbirth at 7 months.
Dylan attributes Rihanna's illness to Brian's smoking, and Hazel eventually admits that he still smokes but only ever outside and wouldn't ever want to harm Rihanna. Dylan phones Brian and tells him to come to the ED as a result of his daughter's condition. Elle speaks with Soph who doesn't want to have a c-section and also that she hasn't felt the baby kicking. She also tells Elle that she's feeling a pain when she breathes in which prompts her to phone the maternity unit for further assistance with the case after she grows concerned. On the maternity ward, Duffy is informed that she's needed in the ED.
Iain arrives in the ED accompanied by Jez and Rita and despite the jokes going around, Rita takes it seriously and tells Iain she'll be treating him herself and that it will give them a chance to catch up. Elle tells Robyn that she wasn't to know that Soph was having problems with the baby and not to blame herself. Charlie overhears and praises Elle for not making Robyn feel that she missed something. Jacob tells Dylan that it's a bacterial infection not caused by second-hand smoke. Brian arrives shortly after and Dylan lies to him and tells him that he's to blame for Rihanna's illness.
Rita treats Iain and confronts him about him trying to get away. She prepares to treat him with a very large needle and although Jez tries to get Iain to tell Rita how he truly feels, he is scared that she'll hurt him with it if he says he doesn't want to be with her. Elle informs Soph that she'll require a CTPA scan in order to determine whether there's a clot in her lung. Soph disagrees, fearing that the radiation could cause harm to the baby as she attributed her previous stillbirth to the CTPA scan she had before. Louise says they could to an echo instead and although Elle disagrees, Soph sees it as an ideal option and they go ahead with it. Elle begins to discuss their plan of action when Soph's husband Liam arrives. He insists that she have the scan anyway and begins shouting at Elle, only to be interrupted by Duffy who's arrived in the ED to assist.
Hazel explains to Brian that the smoke from outside can still travel inside on his clothes and pleads him to stop. This prompts him to go outside for a cigarette as Dylan arrives, claiming that it's his right to do so. Jez speaks to Iain whilst he's recovering and tries getting him to tell Rita the truth but he's still hesitant to. Dylan angrily confronts Brian outside the ED although moments later he collapses and is taken inside. Elle, Duffy and Louise continue Soph's treatment but when her heart rate begins to increase, Elle fears she's taking a turn for the worse and takes control and informs her that they'll have to do the CTPA scan.
Dylan treats Brian and discovers that his lung condition has worsened. Although he informs Jacob that he's not involved in the case, he later gets Ethan to take over to perform a risky procedure. Dylan goes to speak to Hazel and he explains to her that it isn't his fault that his father abandoned him as a child. After the CTPA scan, Elle tells Soph that they found a clot in her lung, but that they're going to keep her on the medication for now as opposed to performing a c-section. Duffy speaks to Liam outside the ED and she empathises with him and explains that it's tough on the father too. They go back inside to see Soph where she's once again deteriorated and is in need of a c-section but they can't get through to her. Duffy explains how essential it is for her to have a c-section which prompts Elle to inform Soph that the anti-coagulation drugs aren't working and she needs one immediately. Although she initially disagrees, Elle manages to convince her to have a c-section, and they all prepare to go up to ITU until an obs and gynae surgeon is available.
As they're on their way to get Soph upstairs, she goes into cardiac arrest and Elle decides to return to the ED. With the obs and gynae team caught up on a twins case, Elle has no choice but to perform the c-section herself. With Soph still in arrest and Louise performing CPR, the baby is successfully taken and moved up to ICU with Duffy and they take Liam with them. Charlie comes upon Duffy who's standing outside the room where Liam and the baby are. They reunite and Duffy explains that New Zealand is still her home, but she has come back for some agency work like she had done last year.
Dylan discharges Brian, and feels that they're on better terms. Brian expresses his appreciation and tells Dylan he wants to make things right. Despite their best efforts, Soph is unable to be resuscitated and the team agree that there's nothing that could be done. Elle goes up to see Liam to inform him that Soph didn't make it, although he's able to guess by her facial expression.
Robyn and David are preparing to leave work when they see Iain recovering in the staff room and Robyn tells him that she knows about him and Rita. Rita soon walks in and goes over to Iain, happy that they're still together. However, Iain admits that sleeping with her the night before was a mistake and that he wants to end it. Rita is shocked, but tells him it's fine before walking away. Duffy prepares to leave and tells Louise not to let the events of the day knock her confidence.
Robyn sees Glen outside the ED and although she presumes things would be awkward after their kiss, he asks her if she'd like to go to the mortality café with him again, leaving her delighted. Charlie speaks with Elle outside the ED and she explains to him that she always tries to make the right decision including telling Hanssen about him. Charlie tells her not to worry and assures her that she did the right thing. Jacob has also become friendlier with her and they agree to go for breakfast together. He also tells her that he was preparing to give a speech earlier that day for a presentation which he is due to give the following week. Duffy goes to get in her car to leave, before waving goodbye to Charlie.
In the week before the episode aired, the BBC posted several new icons and images specially for the 1000th episode, including a new cover photo for their Facebook page. The celebrations for the episode kicked off for the series finale and 30th anniversary. In addition to the promotional images posted by the BBC, the title sequence also differed slightly in the logo for this episode.
Although the 1000th episode was known to be airing at some point towards the end of series 30, it was initially assumed to be the fortieth episode, as that's how it fitted into the episode numbering. However, when the BBC announced Duffy's return, they stated that the 39th episode was actually the 1000th. The source of this difference in numbering was from the series 20 Casualty@Holby City episodes "Teacher's Pet" and "Crash and Burn", which were counted as one episode together. However, the BBC counted them as two separate episodes, resulting in episode lists needing to be amended.
Overall reception to the episode was mixed. Over social media, many fans commented on the fact that the 1000th episode had no real significance in comparison to other episodes aside from the guest apearance of Duffy. Additionally, some fans were critical of the episode as a result of Elle taking centre-stage as they felt that a more prominent character should have has a larger role for the occasion. Writing for the Radio Times, Alison Graham commented "It's the 1000th episode, but there are no balloons, badges or parties. Life and death go on as normal in Holby City Hospital's emergency department."