Episode 20 is the 1112th episode of Casualty and the 20th episode of the 33rd series. It was preceded by Episode 19 and followed by Episode 21. The episode was directed by Paul Riordan and written by Rebecca Wojciechowski.
Alicia receives a letter from City of Manchester Hospital offering her a paediatric fellowship and goes to tell Ethan, but she sees him holding an engagement ring. Connie and Elle congratulate her for being accepted, but Alicia tells them that she may turn it down to be with Ethan.
In the paediatric ED, Alicia treats a young boy called Donnie whose mother Kate fears that he has type 1 diabetes. Louise recognises him and recalls his condition being a mystery, but Kate denies there being any confusion. Once a blood sample is taken, Kate insists on taking Donnie home, making Alicia suspicious. She soon receives Donnie's admission history from St. James and learns from Louise that Kate operates a blog about his condition. When his blood test results contradict his urine test results, she gets her colleagues to help in her investigation. She voices her concerns to Connie and suggests that Kate has been inducing her son's illness, and she agrees with Alicia's decision to call safeguarding. However, when a new blog post is published, Alicia takes matters into her own hands and goes to Kate's house.
Alicia arrives at Kate's house and is horrified to learn that she has been giving Donnie insulin injections. She finds him in his room and tells Kate to call for an ambulance. Alicia runs downstairs for glucagon, but, as she goes back to Donnie's room, Kate demands her to leave. Alicia tries to push past her, but Kate pushes her in a vase. In their tussle, Alicia accidentally pushes Kate down the stairs and leaves her to help Donnie. The paramedics soon arrive, and Alicia manages to convince Kate to let them treat Donnie. They soon arrive at the ED, and they manage to stabilise Donnie.
Connie tells Alicia that she can lead and questions why she would want to turn down the fellowship. Outside, Alicia tells Ethan that she is going to accept the fellowship, and Ethan doesn't mind. He goes down on one knee and proposes to her, but she tells him that it's not the right time. Later, Elle tells Ethan that, if he wants his relationship with Alicia to work, he has to fight for it. He rushes out of the department and finds Alicia, and he tells her that he is going to resign and accompany her to Manchester, but she reminds him that they've constantly let things come between them throughout their relationship. Alicia tells him that she has the chance to do something amazing with her and needs to do it on her own. They share one final kiss before Alicia leaves the ED and Holby for good.
Meanwhile, Marty continues to allow Joshua to believe that Charlotte is his daughter, and they arrange to go out on another date. As he is not on duty, Louise asks Marty to help out, but he reminds her that he is observing the paramedics for the day. He changes his mind and tells her that he can work in the ED. He also agrees to pick up Charlotte from daycare. However, Iain and Ruby force him to come with them. On the road, they reprimand him for his disrespectful attitude towards patients and, when Marty says that he has other commitments, exasperated, Iain leaves him by the side of the road.
Robyn hears that Marty cannot pick up Charlotte and rushes to the daycare. There, Joshua doesn't recognise her and tells her that he is a friend of her father. Robyn assumes that he means Glen, but he tells her that he was referring to Marty. Marty returns to the ED and tells Louise that he wants to learn, but she tells him to go home. He tries to apologise to Robyn, but she doesn't accept it. Elsewhere, Marty finds Joshua and tells him that he is ashamed of himself for lying, but Joshua breaks up with him and asks him to never contact him again. Later, Louise tells Marty to think about the consequences of his actions and reminds them that he doesn't need to prove himself to everybody all the time.
In the afternoon, with her bank account empty, Louise is forced to visit a food bank in the church. There, she bumps into Ernest who is suffering from a very bad cough. She encourages him to go to the ED.