The oldest child and only daughter of Tommy and Angela Harris, the family moved into 6 Coronation Street in November 2002. The family had been placed under a witness protection program under the surname of "Nelson", as Angela was due to testify in a gangland murder trial. When the brothers of the defendant came to Weatherfield, this became common knowledge and the family resumed using the surname Harris. Katy discovered she was diabetic, and nurse Martin Platt helped her get used to giving herself daily injections of insulin. The two developed a romantic relationship, even though Martin was 20 years older than Katy - almost as old as her father. Katy became pregnant, but her scheming father, Tommy, persuaded her to have an abortion by fabricating a story that Martin was having an affair. Tommy hated Martin for sleeping with his beloved daughter, branding him a 'pervert.'
When Katy found out Tommy had lied, she confronted him at the garage, but he showed no sympathy or remorse. On the spur of the moment, she lashed out and hit him over the head with a wrench, killing him.
Katy's mother Angela witnessed the murder but persuaded her not to call the police. They then went through a pretence that Tommy had been killed by an intruder, until forensic evidence led to Angela's arrest. After a few weeks, Katy could live with the guilt no longer and wrote a note telling the truth about her father's death before committing suicide by drinking water mixed with sugar (a deadly solution, because of her diabetes). Martin later found her lying unconscious on the sofa with the note right beside her. She was taken to Weatherfield General but died just after her arrival.
Following Katy's death, Angela was cleared of manslaughter but faced new charges of assisting an offender and conspiring to pervert the course of justice, which meant that she remained in prison.
First and last lines
"Is that it?" (First line)
"That's it." (Final line)