When the couple return from their honeymoon, Katie falls out with her friend Gennie when she reveals that Chas, her half-sister, had been having an affair with Cameron Murray (Dominic Power), leading to Carl, Chas's ex-boyfriend, being killed on Katie's wedding day. After Katie rejects Gennie's attempts to patch things up, she tells Megan and Robbie about Katie setting Robbie up for attacking her. Declan is angered by Katie's actions and begins to mistrust her. He blames her for losing him his family and rides off on a quad bike alone. Katie follows him on another quad and accuses him of changing her for the worst due to his cold, unfeeling demeanor and ruthless nature. Katie rides off angrily but crashes the quad bike and falls down a disused mine shaft. She initially lands on a ledge but Declan's attempts to rescue her fail and the ledge gives way and she falls the rest of the way down to the bottom of the shaft. Trapped and badly injured, Katie crawls through the tunnels in the darkness as a full scale rescue operation is mounted. After days of searching, Declan begins to lose hope of finding Katie alive. She is eventually found by Sam Dingle (James Hooton) in a shaft under the moors in a critical condition. Katie is hospitalised in a critical condition and goes into cardiac arrest but is resuscitated. When Katie finally regains consciousness, she recalls her argument with Declan from before the accident. The couple apologize to each other over their respective actions and Katie returns home, initially walking on crutches. Katie later collapses and is returned to hospital where she is discovered to have damage to her ovaries caused by her injuring her pelvis during the accident. She if left infertile and unable to have children. Declan tells Katie that is doesn't matter but he is secretly disappointed as he had wanted a son to inherit his fortune. Katie begins to regret marrying Declan and she decides to leave indefinitely after talking to Andy about her problems..