Time in the Emergency Department (2005-07)
Nathan began his time at Casualty by stalking Selena Donovan. He was at one point jabbed with a needle which could possibly have been used by an HIV-positive patient. Nathan ordered a search of all clinical waste to find the needle and became more uptight than usual, with receptionist Alice Chantrey bearing the brunt of his anger. However, after being persuaded to take an HIV-test, Nathan was relieved to be given the all-clear. After starting a relationship with Selena, Nathan proposed marriage to her.
Displaying character traits of being a jobsworth and a stickler for the rules, Nathan took great pleasure in installing a large plasma TV screen in the middle of the department to enforce the "four-hour rule", a government directive in which 98% of all A&E patients must be seen, treated, and admitted/discharged within four hours of arrival. However, in blatant disregard of his own rules, on one occasion Nathan had his own mother admitted ahead of all those currently queued in the system. Harry Harper continued to clash with Nathan, so in another attempt to get rid of him, Nathan fabricated a charge of sexual harassment against him and persuaded Alice to make a complaint. Harry was suspended, but Alice became suspicious and withdrew her allegation when it threatened to devastate Harry's election campaign. Nathan was forced to confess all to Selena, who ended their engagement.
When Harry was unexpectedly elected as Holby's new MP (he stood for Parliament in a bid to save the Emergency Department from closure), Nathan installed wildcard Australian Theo "Stitch" Lambert as the new consultant. When he discovered Stitch in his office taking cocaine, he was convinced to keep quiet by the threat of the ridicule which would ensue if it was revealed Nathan had made such a poor staffing choice.
Later on in the series, Selena discovered she was pregnant with his baby. She informed Nathan that she had had an abortion, however later revealed to Harry that she had not actually done so. Nathan remained unaware of this until the last episode in the series, when Selena was shot dead. The team performed a Cesarean section on Selena, delivering her and Nathan a baby daughter, Angel. Angel later died in Nathan's arms after being diagnosed with a severe E. Coli infection in the NICU and he switched off her ventilator.
Nathan left the show in episode six of series 22. He was sacked for incompetence by Harry Harper, now having quit Westminster to return as the Emergency Department's consultant manager. Despite their previous working relationship Harry found the job difficult, knowing what Nathan had recently been through.