Simon joined Holby A&E as a locum in series 16, following Patrick's death. He got off to a bad start with the grieving Lara by introducing himself as "the new Patrick Spiller". They argued over patients and found they were up against each other for the permanent SPR post. Simon bumped into his ex-girlfriend Claire when she turned up in A&E after a squash injury, and discovered she was engaged to his younger brother Stuart. Simon and Stuart did not get on, as Stuart was jealous of his older brother, feeling that Simon was always their parents' favourite, but Claire convinced them to make peace. There was still a spark between Simon and Claire, however, and they started an affair. Stuart and Claire's wedding was approaching fast, however, and Stuart asked Simon to be his best man. The day before the wedding, Claire came to see him, saying she couldn't go through with it. Simon told her she couldn't pull out now, and lied that it was only a fling. He hadn't planned on staying in Holby, but to his surprise he got the registrar's job, and accepted so as not to have a black mark on his CV.
On the day of the wedding, Stuart turned up in A&E, almost prepared to kill Simon after Claire told him everything. After a fight, Claire admitted to Stuart that she loved Simon more, and Stuart walked out on them. Simon asked Claire if they could start again, saying he had been lying yesterday, but Claire didn't want to give him the chance to let her down again, and left.
At the beginning of series 17, Simon was attracted to locum SHO Heather Lincoln, but though Heather flirted with him, it was Dillon she went out with. When Dillon cancelled their date one evening, however, Heather asked Simon out, and they spent the night together. On finding out what had happened, Dillon banged Simon's head against a locker and thumped him in the stomach, saying, 'That's for sleeping with Heather.' Simon got a dressing-down from Harry about his behaviour, but Simon wasn't too bothered, feeling that he had got one over on Dillon, and still had Heather. But Heather had other ideas - she told him he was just a fling.
Simon had always got on well with Colette Griffiths, and it was Simon she turned to when she and Josh had problems with their marriage. When Josh, dealing with a man who had lost his family in a car crash, called off their evening at a charity auction, Colette asked Simon instead. Simon bought her an expensive necklace, and had persuaded her to go for a few drinks afterwards when Josh arrived to pick her up. When Josh was late for the Christmas party, Colette again turned to Simon, and they ended up sleeping together. Simon afterwards said it was a mistake, and was worried when Colette left Josh soon afterwards. Determined to show Colette she meant nothing to him, Simon went out to meet someone new, and met Jane Winter. She didn't make things easy for him and Simon was shocked to discover she earned her living as a high-class escort. But he was determined to make things work with Jane, and told her he could shut that part of her life out of his mind. He couldn't manage it, however, and gave Jane an ultimatum - her 'job' or him. He told her he loved her, and Jane eventually gave up escorting. Soon afterwards however he rushed her into A&E when she collapsed, and it turned out that she had a brain tumour. The operation to remove it left Jane paralysed, and she wanted Simon to stand by the promise he'd made to leave her if that happened, but Simon wouldn't.