One storyline sees CT1 doctor Dominic Copeland (David Ames) attacked by an aggressive partner, who is married.
A prominent storyline in the series is CT2 doctor Arthur Digby's (Rob Ostlere) melanoma diagnosis, which proves to be terminal.
Series 18 of Holby City attracted 4.5 million viewers on average with three episodes failing to reach the top 30 rated programmes of the week.
Four cast members and three storylines were nominated at the 2016 Inside Soap Awards, and Ostlere won the "Best Drama Star" accolade.
The episode centres around junior doctors, Arthur Digby (Rob Ostlere), Morven Shreve (Eleanor Fanyinka), Oliver Valentine (James Anderson) and Zosia March (Camilla Arfwedson), and Harper confirmed that it would answer several "'will they, won't they?'
Harper confirmed this series would feature crossovers with the show, especially around the time of Casualty's thirtieth anniversary in September 2016.
[64] On 28 June 2016, it was announced that Marcel, Henry and Alex Walkinshaw would guest appear in Casualty's feature-length anniversary episode "Too Old for This Shift", originally broadcast on 27 August 2016, as their characters Jac, Hanssen and Adrian "Fletch" Fletcher respectively.
[68] In an October 2015 interview with Daniel Kilkelly of Digital Spy, Harper revealed a selection of upcoming storylines to feature in the series.
[59] He explained that a "dramatic and exciting" twist in a storyline involving Cara Martinez (Niamh Walsh) and her husband, Jed Martinez (Jody Latham), would challenge Cara's relationship with Raf di Lucca (Joe McFadden), while a theme of "people's pasts coming back to haunt them" would be explored with the characters of Mo Effanga (Chizzy Akudolu) and Serena Campbell (Catherine Russell).
[59] Harper also announced plans to explore the on-again, off-again relationships between audience favourites Zosia and Oliver, Arthur and Morven, Sacha Levy (Bob Barrett) and Essie Harrison (Kaye Wragg), and Mo and Mr T, adding that they would answer some ongoing questions in late 2015.
[70] In his October 2015 interview with Kilkelly, Harper teased a "heartbreaking and touching" storyline to air in 2016 which would bring together every character.
[59] This storyline commenced in February 2016 when Arthur is tested as a liver donor for Morven's father, Austin Shreve (Clinton Blake).
Guy Henry appeared as Henrik Hanssen, the hospital's chief executive officer and consultant general surgeon.
Catherine Russell played deputy chief executive officer, clinical lead of the Acute Assessment Unit (AAU) and consultant general surgeon Serena Campbell.
Alex Walkinshaw starred as AAU ward manager Adrian Fletcher, while Kaye Wragg appeared as staff nurse and transplant co-ordinator Essie Harrison.
Additionally, Ben Hull and Carli Norris continued their semi-regular roles as Derwood "Mr T" Thompson, a consultant obstetrician and gynaecologist, and agency nurse Fran Reynolds.
[41] After taking maternity leave in April 2015, Rosie Marcel returned to her role as consultant cardiothoracic surgeon Jac Naylor in November 2015.
[9] Hugh Quarshie's return in the role of consultant general surgeon Ric Griffin was confirmed in October 2015, following his break during the previous series.
[15] Jimmy Akingbola and Lauren Drummond reprised their roles as Antoine Malick and Chantelle Lane respectively for a cameo appearance in episode 35.
[68] On 3 September 2015, it was announced that actress Jemma Redgrave would join the cast as "feisty" general surgeon Bernie Wolfe, who has experience working in the army.
[80] Marc Elliott's casting in the role of Isaac Mayfield, a "charming, confident and twinkly" doctor, was announced in April 2016.
"[82] Episode 48 marked the first appearance of Inga Olsen (Kaisa Hammarlund), Mr T's fiancée who works as a bank nurse on Darwin ward.
Jody Latham continued his role of Jed Martinez, the husband of Cara, from the previous series, departing in episode 6.
[59] Rupert Frazer appeared between episodes 22 and 27 as Sir Dennis Hopkins-Clarke, a consultant cardiothoracic surgeon working on Darwin ward.
Rachel Sigee of Evening Standard believed that his introduction would begin "a breakthrough year for actors with autism".
The introduction of Jasmine Burrows (episode 41) was enjoyed by Vicki Power (Daily Express), who described her entrance as "memorable" and "like a shot in the arm for the medical soap".
[90] Victoria Wilson (What's on TV) called the scene where Fletch asks Raf to care for his children if he dies (episode 49) "heart-breaking".
", and "Zosia and Ollie's romance" were longlisted in the "Best Drama Storyline" category;[98] the first two were then shortlisted and "Arthur's death" was announced as winner.
On 17 November 2015, episode 6 received 3.64 million viewers and a 15.8% share of the viewing audience, a drop in ratings due to clashing with a football match.
[8] Despite being above the series average, episode 11, broadcast on 22 December 2015, failed to reach the top 30 rated programmes with 4.54 million viewers and a 21.2% share of the viewing audience.