"Little Sister" is the 1023rd episode of Casualty and the 19th episode of the 31st series. It was preceded by "Back to School" and followed by "Crazy Little Thing Called Love". The episode was directed by Fiona Walton and written by Jeff Povey and Joseph Wilde.
A teenage girl named Gemma is on day-release from a young offenders' institute with her supervisor Belle. In the kitchen at a local event, Gemma hits Belle over the head with a frying pan when she irritates her. In a panic, Gemma calls for an ambulance but hides when the paramedics arrive. However, on her way out she falls down the stairs, injuring her chest and abdomen.
Meanwhile, Jacob moves out and Connie is upset. However, they're thrown together at work when they treat a man in his mid-60s, Jamieson. However, he claims to be in his 30s and when his much younger fiancée turns up, Connie's suspicions are soon raised. Things only worsen when his fiancée Kristina gets their solicitor into the hospital so he can sign the will. Elsewhere, Cal tries to get onto Alicia's phone, as he's sure that she's seeing someone else. However, Charlie catches him in the act and persuades him to hand it over.
Once Belle has been admitted, Gemma goes to the ambulance station and finds Iain, whom she recognised from earlier. Iain recognises her as his younger sister and she tells him that it's the day of their grandfather's funeral. She's angry when she discovers that he's been back from Afghanistan for a number of years and never bothered to see her and their mother. Iain soon realises her injuries and gets her admitted. It's also the day that Robyn finds out about whether her baby is healthy with a scan.
Lily treats Belle and Gemma and soon makes a connection between the two when she notices Belle speaking to her. However, Belle was actually threatening Gemma which results in her making a break for it to go to her grandfather's funeral. Iain is concerned as she has a pneumothorax, and insists to Jez that they have to track her down. They leave for the cemetery in the ambulance in search of her.
Meanwhile, Elle receives a tip-off that the Trust aren't taking Connie's case any further and is delighted. However, she's also intent on enforcing a three-hour rule in the department in an attempt to free up more beds. Noticing that Jamieson's scan results are all clear, she gives the order to discharge him. However, as he's leaving Jamieson collapses in reception and it transpires that he had a piece of denture stuck in his throat. Connie is furious that Elle discharged his patient.
It's not long before Jamieson realises the truth and he tells Kristina to leave. She takes some money from his wallet and leaves. Connie apologises to Jamieson again for him being discharged. She gives him a form and advises him to make an official complaint if he is unhappy, in one last attempt to get Elle in more trouble. Meanwhile, Robyn discovers that everything is okay with her baby. Connie returns home to find that Grace has been able to walk up some stairs by herself and get dressed.
Iain finds Gemma at the cemetery and brings her back to the ED after they share a chat about what he's missed. However, whilst they were gone Lily has discovered that some of Gemma's marks from earlier match those of Belle's rings. Lily calls the police on Belle, whilst also getting Gemma in trouble. Gemma is taken away by the police, but Lily is unsatisfied due to the fact they didn't believe her about Belle's abuse of Gemma. Iain is angry with Lily for this as he storms off to continue his shift.