On 5 December 2017, with the imminent arrival of the eminent neurosurgeon John Gaskell, Ollie was galled after Jac shifted all of her procedures onto him and humiliated in theatre when she started harshly disparaging his abilities as a surgeon. His frustration intensified when he discovered that Roxanna had abandoned her virtual reality project after deeming David to be an unviable candidate. Following a confrontation with Roxanna on Keller, Lofty tried to express his concerns to Ollie about David's condition and temperament, but Ollie was not interested. On Darwin, Ollie handed Jac his letter of resignation; when she attempted to discuss her reservations about Gaskell's trial, Ollie asserted that he was owed an apology.
Later, as Ollie and David observed Jac and Gaskell in theatre, David began to have a stroke and was taken onto the ward. After it was discovered that David had a patent foramen ovale that was exacerbating his dementia, Jac allowed Ollie to operate on David and apologised to him, assuring him that it was his duty to stay and become a CT consultant; Ollie quickly realised that she was intending to resign. (HC: "Group Animal - Part One")
During David's operation, the theatre staff learned that a man had entered the hospital with a gun, but David and Roxanna insisted on continuing. However, when the gunman - Fredrik Johanssen - entered the room, he shot Ollie in the head, macerating his frontal lobe. Although Roxanna initially continued operating on David, Morven, who was observing the procedure, urged her to prioritise Ollie. Roxanna eventually agreed and managed to stabilise him; once the hospital was taken off lockdown, Ollie was moved to ITU. (HC: "Group Animal - Part Two")