"A Clear Conscience" is the 993rd episode of Casualty and the 32nd episode of the 30th series. It was preceded by "Survivors" and followed by "Tangled Webs We Weave". The episode was directed by Lee Haven Jones and written by Joe Williams. It featured the final appearance of Jack Diamond portrayed by Alistair Brammer who joined the show in December 2015.
Ethan and Cal arrive for work, and Ethan once again amuses his colleagues with his attempt to be more adventurous when he reveals that he has taken up salsa classes. Big Mac follows shortly after, and immediately gets angry with Jack when he makes a joke about him tripping over a mop bucket. Rita tells Iain about Mark being there the week before and apologises for not telling him sooner. She also realises her ID badge has gone missing. Soon after, Connie comes into her office to inform her that a complaint has been lodged against her by a patient and although Rita claims she has no knowledge of the patient or the behaviour stated in the complaint, Connie is still annoyed.
Elsewhere in Holby, two young men Kash and Leon are told they owe another man named Zeke a favour, who feels that they're in debt to him as he served jail time previously without getting them in trouble. He sends them to go to a local dig site to rob it and gives them a gun. They arrive after dark but Leon finds himself unable to do it and they decide to walk away. He also informs Kash that he's got them both a job working at the dig site. However, just before getting in the car they alert the site manager Steve of a smell of gas. He orders a halt to all operations but one of the men, Phil, is unable to control his digger and it begins to spin around. It knocks the gas pipe and causes a huge explosion which results in Leon becoming severely injured.
Back at the ED, Big Mac once again encounters Mercedes who instructs him to get her more drugs. However, he tells her that Charlie and Rita are getting suspicious and are watching the supplies carefully after they notice stock levels and the amount given to patients not adding up. She refuses to believe him and threatens to tell everyone that he's been stealing if he doesn't get her some. Jack's day gets even worse when a patient vomits on his shoes.
Meanwhile, the casualties from the dig site arrive at the ED. After being checked over, John admits to Louise that he had expressed concerns about the safety of the digger before use but his boss had instructed him to use it anyway. Steve later comes to see him and tells him that if he reveals the health and safety error to the police, he'll lose his job. He later offers him a £10,000 bribe not to tell, and increases it to £20,000 out of desperation when he is reluctant to comply. Phil eventually decides to tell the truth and forfeit his job and the bribe in order to do what's best for his two daughters, Sam and Georgie. Meanwhile, Zoe starts to compose an email to Nick Jordan to ask if there's any jobs available in America with him. She's interrupted by Max and goes on her online dating profile instead. He isn't bothered by it and they almost share a romantic moment together but Max leaves the room.
Kash accompanies Leon into the ED, and is later confronted by and angry Zeke who turns up. Zeke threatens Kash, but he's chased towards the exit by Rita as she tells him not to return. Kash attempts to hide the gun which he took possession of after Leon was injured. Meanwhile, Dylan and Cal treat Leon whose injures are more extensive. They perform a risky procedure which goes seemingly well, but he later takes a turn for the worse and dies. Kash and Zeke watch on and the situation soon erupts when Phil admits that he was the one driving the digger, and is held at gunpoint by Zeke. Kash soon gets his hands on the gun, but drops it with advice from Rita and Big Mac, and the police step in to apprehend Zeke.
Rita discovers that the patient who made the complaint didn't actually exist, and also receives a threatening text and assumes it's from Mark, still angry at her for contributing to his breakup. She is horrified when she realises her computer screen has been smashed, but Zeke soon implies he is responsible which makes Rita reconsider her accusation of Mark. Big Mac is confronted again by Mercedes outside the ED, and she threatens him once again and he says he will do what he can. He goes into Charlie and Rita's office and phones the pharmacy to order more tramadol. Just before he arrives to collect it, he's confronted by a suspicious Charlie who explains that he thinks there's a thief amongst the staff. Mac is therefore unable to acquire the drugs for Mercedes, and now fears for his career should she reveal his secret.
Noel finds Mac outside the ED, and he confesses everything to him, including the fact he's the one who's been taking the tramadol. Noel later confronts Mercedes, and tells her that Mac won't be getting her drugs anymore and to leave them alone. She once again threatens to tell, but he explains that she's already got the upcoming court case regarding the mugging back in January, and that she doesn't need another. Noel sets Mac up for a session at an NA meeting to help him, but just as he's about to enter he has second thoughts and turns away.
Jack says goodbye to his colleagues outside and is splashed by a car when it goes through a puddle soon after, therefore topping off his bad luck for the day. Rita returns home and is horrified when she goes upstairs to find that her bedroom has been trashed. She finds her ID badge in her room with the name scribbled out. She turns round to leave and is left even more terrified to see the words "you will suffer" written in lipstick on her mirror.