Tess Harris (neé Merton) was Leo Goskirk's teaching assistant and had an affair with Leo's step-father Paddy Kirk. She died in February 2016 after accidentally being ran over by Kirin Kotecha while he was drink driving.
Paddy and best friend, Marlon Dingle, met Tess and her friend Chloe on a night out. Paddy insulted Tess and left the bar. He went to get his coat and tried to step in when a man took Tess's leather jacket from the cloakroom. The man walked away and Paddy and Tess were thrown out of the club. Tess offered to give Paddy a lift home but they sat in Tess car and talked about Paddy's problems with Aaron. Paddy explained about Aaron's disastrous relationship with Robert which culminated in Paddy being shot and Leo being threatened. He explained that he could not go to the police as Aaron would get into trouble too, and even his wife Rhona didn't know he was shot. Tess assured Paddy he was not a coward and they kissed and had sex in the back seat despite them both being married. Tess offered to take Paddy home but he declined and they both regretted their liaison.
Paddy tried to move on but they had an awkward reunion when Rhona introduced her as Leo's teacher. Paddy was unhappy about this and Tess tried to find another teacher for Leo, but after he acted out at school, Tess resumed teaching him.
Paddy was unhappy with Rhona's desire to have another child, only reluctantly agreeing to look into adopting. His unhappiness, Tess' unhappiness with her husband Pierce, and their mutual attraction led them to rekindle their affair. Their relationship was very tumultuous. Paddy tried to end it after a hotel room encounter where Rhona almost caught them. Later, Paddy mistakenly assumed Tess had told social services that he and Rhona were not ready to adopt and angrily confronted her, only to realise that Aaron was responsible. Paddy ended things with Tess so she flirted with Marlon to make him jealous, leading Paddy to berate Marlon for being interested in a married woman.
In spite of everything, Tess still had strong feelings for Paddy and finally decided to tell Rhona everything. As she went to do that, she was knocked down by a drunken Kirin Kotecha. Paddy and Rhona found her by the road and while Rhona called an ambulance, Tess told Paddy that she loved him, before losing consciousness. Rushed into surgery, doctors were ultimately unable to save her and she died, leaving Paddy and Pierce heartbroken. Just days after Tess's death, Paddy revealed their affair to everybody.