Kat gives birth to Tommy, and is rushed to hospital the next day due to complications. While she and Alfie are absent, James, the newborn son of local resident Ronnie Branning (Samantha Womack), dies of sudden infant death syndrome. Ronnie swaps the babies in an act of desperation. A devastated Kat believes her father is to blame for Tommy's death, as he left him alone to go for a drink. After the funeral, Ronnie attempts to return Tommy, but Kat misunderstands and believes that she is rejecting James. Charlie opts to leave Walford, although Kat forgives him before he departs. She is shocked when Michael returns to see his son, and upset when he shows no emotion at learning that he died. Kat's friend Martina Quinn (Tamara Wall) and her daughter Shenice (Lily Harvey) visit from Spain. After they leave, Kat and Alfie miss Shenice, and consider IVF to try for another baby. Their consultant feels it is too soon, and their relationship breaks down again, but eventually they reconcile. Four months after taking Tommy, Ronnie returns him and hands herself in to the police. Kat reacts with disbelief, but a DNA test reveals the truth, and Kat is reunited with Tommy. Kat is initially furious with Ronnie, but forgives her when she is sentenced to three years in prison.