kate mitchell, played by jill halfpenny, is an undercover policewoman who grows close to phil mitchell (steve mcfadden) to extract a confession of murder from him. however phil is innocent, and once the truth is revealed the couple begin a relationship and soon marry. however the marriage ends, and kate then has an affair with den watts (leslie grantham), phil's arch-rival and the husband of her business partner, chrissie (tracy ann oberman).