At some point, heroin addict Michelle Gibson was prescribed methadone to help combat her addiction, but Kostas started offering her excessive doses, resulting in her becoming addicted to methadone. On 28 July 2019, she held him at knifepoint and forced him to give her several boxes of oral methadone and the money from the pharmacy's till, but consultant Connie Beauchamp walked in to hand in a diazepam prescription. He told her that it was not a convenient time, but she insisted on having her prescription filled. He reluctantly gave her the drugs and instructed her to leave, but registrar Archie Hudson appeared and proceeded to call the police on Connie. However, Michelle threatened Kostas and ordered her not to call them.
As Kostas capitulated to Michelle's demands, Connie treated her infected track marks, and Michelle revealed that Kostas was responsible for her addiction. Furious, he attacked her with a baseball bat, and she slashed his arm in self-defence. Once Michelle fled, Kostas was hesitant to call for an ambulance, but, as Archie had sustained a serious stab wound, Connie pleaded him to call for one, and he reluctantly agreed. When Archie began presenting with a tension pneumothorax, Connie instructed him to fetch a large bore needle to decompress it. The paramedics soon arrived and tended to Kostas' injury. (CAS: Episode 1138)