Paul McGann made his first appearance as John Gaskell on 5 December 2017. His casting was announced in April 2017. He came to Holby after curing a man's MND via stem cells which allowed him to walk again, which was met by some disbelief from his colleagues until he brought the man in. He later assisted Sacha Levy and Essie treatJac Naylor after she was shot by Fredrik Johanssen by packing her with tampons and stopping a bleed by using an innovative although untested patch. He was later shown comforting Sacha when he found Raf dead in a lift. Later on, he asked Essie to scrub in on a surgery he was performing and they had a deep conversation.
On the day of his death, he was being found out for his murder of Roxanna MacMillan by Meena, Zav, Sacha, Ric, Fletch, Essie and Serena. He also tried to murder Jac Naylor (with MPTP) and Essie Di Lucca (with Diazepam). Before he left the hospital, he left Lana, his first trial patient, in surgery all opened up where she was found by Henrik, Sacha, Ric and Fletch. They saved her but she couldn't live without life support and later died, also down to the actions of Gaskell. Rather than facing up to his problems, he decided to go to a nearby lake and drown himself. Before he did it, Henrik Hanssen found him and tried to talk him out of killing himself. Then, Gaskell told Henrik absolutely everything about murdering Roxanna and trying to murder Jac. He then walked underneath the water and died.