Timothy does not appear in Series One. He is first introduced in the 2012 Christmas Special as Dr Turner's mischievous, though kindhearted and understanding, son. As Series Two goes on, it is apparent that he is very fond of Sister Bernadette, particularly when she helps him win the three-legged race during a fete. He sends Sister Bernadette letters during her stay in the sanatorium as she is treated for TB, and sends her a dead butterfly in a match box, hoping to learn the cause of its death. Timothy frequently shows a fascination with medicine and the human body. He is also skilled in playing piano and violin.
When Sister Bernadette leaves the Order and reverts to her birth name, Shelagh, Timothy knows that his father is in love with her, and approves. He goes with his father to pick her up from the sanatorium, and, when Patrick decides to propose, he writes a note saying "Please will you marry my dad?" wrapped around the ring box. During the 2013 Christmas Special, he contracts polio before his father's wedding and nearly dies. Shelagh is distraught and feels responsible, but is comforted by Sister Julienne and visits him with Patrick. Neither show any blame towards her.
Timothy pulls through his illness, but polio subsequently damaged his legs, requiring him to walk in braces. Shelagh becomes fiercely protective of him during this time, especially after she finds out she cannot have children of her own. She does not want him out playing rough games with other boys, but Patrick insists he is an eleven year old boy who needs to have freedom to grow. Shelagh loosens her hold, but she still shows her worry for Timothy occasionally. Timothy is soon able to walk again without the braces.
When the Turners get word from the adoption agency that there is a baby waiting for them to adopt, Tim is excited but says that the way the baby is coming to them (a teenage mother forced to give it up by her parents) is horrible. Timothy shows to be a very good brother to his new sister, Angela, never treating her different or showing signs of jealousy. He loves both Angela and Shelagh dearly.
As Tim gets older, he shows an increasing interest in medicine. He often reads his father's copies of The Lancet and frequently draws his father's attention to articles relevant to conversations or cases that are happening at the time.
In the 2016 Christmas Special, Timothy and Angela are left in the care of Granny Parker while their parents go to South Africa to save a struggling hospital from closure. At Shelagh's request, Sister Monica Joan sends them Timothy's old leg braces which Patrick gives to a boy with polio to help him walk.