Katie Mitchell is the daughter of Phil Mitchell and also Louise's twin sister. She returns to Albert square after she is kicked out of private school. Katie returns to the square and causes trouble. She gets into fights and is a full on Mitchell with a reputation of boys and petty crime. Katie is soon reunited with her cousin Kenadee and they cause trouble together. Soon Katie mets martin fowler and they start an affair together. Katie knows that its wrong but she can't seem to help herself. Even though Martin is a married man he seems to fight himself back with Katie. But for how long can Katie and martin keep up an affair and just how will Phil react when he learns who has been fooling around with his sixteen year old daughter?