Nina Karnik is the former medical director of Holby City Hospital and a consultant general surgeon who worked on the hospital's Acute Assessment Unit from May to August 2017 then Keller Ward from August to November 2017.

Time at Holby City Hospital (2017)

Nina first appeared on 9 May 2017 as a friend of a patient. She also came to talk to his husband she's separated from, Matteo Rossini. Nina and Matteo have a son, Nico, who went missing in 2007 when he was 5 years old and has not been seen since. Nina wants to sell the family home but Matteo doesn't, worrying that Nico might come back to the house and see people he doesn't know and feel that his parents have forgotten him. Matteo agrees to sell it ultimatly.

Nina replaces Serena Campbell as a locum consultant general surgeon on AAU. CEO Henrik Hanssen is impressed by her good work and offers her a full time job which she takes. Nina possesed a folder which contains information about his son's dissapearence. Matteo wants the folder to be demolished as according to him it contains only the pain he and Nina went through and commenting on the folder: "He is not here! Tell me where is he?!" and she find the very last paper between the folder which is a drawing drawn by Nico and she responds: "Found him." Nina burns the folder later with Matteo.

After Sam Strachan's resignation as medical director, Nina applies for the job and she is appointed by Hanssen. Nina wants to divorce from Matteo but he persuades her not to which leads to them sharing a passionate kiss. Nina's first day as medical director was shown in series 19 episode 43 "The Evolution of Woman". She got Guy Self to pitch at the commissioners for a way to decrease obsessive-compulsive disorder surgically which on a trial patient was a success. When Nina wants to cancel the operation, Guy threatens her to speak to Matteo about something 'he stopped her from doing in Berlin'. By episode 44 "Go Ugly Early", the board have decided to close down AAU's Trauma Unit and as Nina wants to excercise her authority on the ward, she is the bearer of bad news and tells clinical lead Ric Griffin and Trauma Unit lead Bernie Wolfe that the trauma section will be closed, ultimately leading to Bernie's resignation.

In series 19 episode 55 "Things Left Unsaid" Nina confesses to Matteo that she hired a private investigator when their son went missing possibly suspecting Matteo having something to do with his dissapearence. Matteo ends their relationship.

When Keller locum registrar Fredrik Johanssen and registrar Dominic Copeland go head to head for the Junior Doctor Award, Nina agrees to mentor Fredrik. He discovers that Nina is pregnant and she asks him to keep it from Matteo. Fredrik's wife Sara leaves him and he falls in love with Nina. When Dominic gets the award, Fredrik tries kissing Nina in Albie's bar but Nina pushes him away saying they're just friends. Fredrik, feeling extremely frustrated gets his revenge by telling Matteo about the baby before leaving Holby.

Matteo and Nina reconcile and do the 12 weeks scan together. They decide to leave Holby and put the past behind them.