Kathy Warren was a private nurse working for the St. Johns. One night while she was out, Peter St. John died, and when it was determined to be murder, she was the prime suspect. She hired Matlock to defend her, offering her engagement ring as a fee. After Lacey St. John told A.D.A. Julie March that the ring had been stolen from their home, Matlock realised that something wasn't right in the St. John house, and that someone was lying to him. (thetvdb.com)